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BRITISH AVONIAN (CARBONIFEROUS) 

CONODONT FAUNAS, AND THEIR 

VALUE IN LOCAL AND 

INTERCONTINENTAL CORRELATION 



F. H. T. RHODES, 
R. L. AUSTIN, and E. C. DRUCE 



BULLETIN OF 
THE BRITISH MUSEUM (NATURAL HISTORY) 
GEOLOGY SUPPLEMENT 5 

LONDON : 1969 



BRITISH AVONIAN (CARBONIFEROUS) 
CONODONT FAUNAS, AND THEIR VALUE 

IN LOCAL AND 
INTERCONTINENTAL CORRELATION 



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BY 



FRANK HAROLD TREVOR RHODES^ RONALD LEYSHON AUSTIN 

and EDRIC CHARLES DRUCE 



31 Plates; 92 Text- figures 



BULLETIN OF 

THE BRITISH MUSEUM (NATURAL HISTORY) 

GEOLOGY SUPPLEMENT 5 

LONDON : 1969 



THE BULLETIN OF THE BRITISH MUSEUM 

(natural history), instituted in 1949, is issued 
in five series corresponding to the Departments of the 
Museum, and an Historical scries. 

Parts will appear at irregular intervals as they 
become ready. Volumes will contain about three or 
four hundred pages, and will not necessarily be com- 
pleted within one calendar year. 

In 1965 a separate supplementary series of longer 
papers was instituted, numbered serially for each 
Department. 

This paper is Supplement No. 5 of the Geological 
(Palaeontological) series. The abbreviated titles of 
periodicals cited follow those of the World List of 
Scientific Periodicals. 

World List abbreviation : 
Bull. Br. Mus. nat. Hist. (Geol.) 



Trustees of the British Museum (Natural History) 1969 



TRUSTEES OF THE 
BRITISH MUSEUM (NATURAL HISTORY) 

Issued 21 February 1969 Price £11 



BRITISH AVONIAN (CARBONIFEROUS) 
CONODONT FAUNAS, AND THEIR 

VALUE IN LOCAL AND 
INTERCONTINENTAL CORRELATION 

By F. H. T. RHODES, R. L. AUSTIN & E. C. DRUCE 



I. 
II. 



III. 



IV. 

v. 



VI. 

VII. 

VIII. 

IX. 

X. 



XI. 



CONTENTS 

Purpose and scope of present study . 

History of previous research .... 

(a) Conodont research in Britain .... 

(b) Carboniferous conodont zonation and correlation 
Stratigraphy ....... 

(a) Introduction to the stratigraphy of the Carboniferous of 

Britain 

(b) The Avonian succession 

(c) Previous research on the correlation of the Avonian with 

the Carboniferous of Europe 

(d) The stratigraphy of areas from which conodonts are 

described .... 
(i) The Avon Gorge, Bristol 
(ii) South Wales 
(iii) Shropshire 
(iv) Yorkshire 
(v) Scotland 
Methods of study 
Conodont faunas 

(a) General Review 

(b) Stratigraphical distribution of conodont faunas 

(c) Avonian conodont biostratigraphical zones 

(d) Intra-Avonian correlation in Britain 

(i) Avon Gorge — North Crop 
(ii) Farlow ..... 
(iii) Yorkshire ..... 
(iv) Scotland ...... 

(e) Correlation of the Avonian with Europe and North America 
Systematic palaeontology . 
Summary and conclusions . 
Acknowledgments 
References ..... 
Appendix ..... 

(a) Sample Register . 

(b) Register of Figured Specimens 
Index ...... 



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65 

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278 

279 
292 
292 
293 
305 



BRITISH AVONIAN CONODONT FAUNAS 



ABSTRACT 

The conodont faunas of the Lower Carboniferous of the South West Province, the 
Yoredales and the Midland Valley of Scotland are described. A complete series of 
samples was collected from the Avon Gorge section, Bristol, and also from composite 
sections from the North Crop of the South Wales Coalfield, the Clee Hills, Wensley- 
dale, Dunbar, Fife, Roxburgh, Midlothian, Ayrshire and Argyll. A total of over 
600 samples was collected at intervals ranging from ten feet (Avon Gorge) to six 
inches (Dunbar). The calcareous samples were dissolved in either 8% acetic acid or 
15% formic acid, and the argillaceous samples subjected to 100 vol. hydrogen 
peroxide. Some 3 tons of rock was processed. 

All collected sections are illustrated and charts of the conodont abundance (number 
of specimens per kilog.) and weight of rock dissolved, together with sample numbers, 
are presented. In all, the samples yielded over 25,000 identifiable specimens, 
referable to 167 species, belonging to 29 genera, of which 2 named genera (Clydag- 
nathus and Patrognathus) , 40 species and 13 subspecies are new. All species are 
described and illustrated, and range charts of their vertical distribution are pre- 
sented. 

The faunas are divided into a total of 14 conodont assemblage zones and correla- 
tions are made between standard sections in the various Carboniferous provinces of 
Great Britain. There is a strong general similarity between the succession of 
conodont faunas in North America, Germany and Britain, although there are also 
some striking local differences. These are analysed in the light of conodont phylo- 
geny, distribution, and of possible sedimentary breaks in various sections. Correla- 
tions are made with the standard goniatite sections of Germany and with the type 
sections of the Mississippi Valley. 

Within the South West Province the basal part of the K Zone is correlated with the 
Cu I goniatite zone and the upper part with Cu II a ; the uppermost K to the Upper 
S2 Subzone is correlated with the Cu II Zone, and the D 1( D2, and D 3 Subzones with 
the Cu III goniatite zone. 

The upper part of the Calciferous Sandstone Measures of the Midland Valley of 
Scotland is of Cu III a age, the Lower Limestone Group is of Cu III (3-y age, and the 
Upper Limestone Group is of E1-E2 (Namurian) age. 

I. PURPOSE AND SCOPE OF PRESENT STUDY 

Conodonts were first described in 1856, and, although they were described in only 
a few papers in the subsequent seventy-five years, there is now a total of some 1,200 
publications devoted to them. Doubt and controversy concerning their function 
and affinities remain greater now than a century ago. One recent author (Fahlbusch, 
1964 ; see also Beckmann et at., 1965) has argued that they represent algae, and 
another that they were internal supports in some ciliated tentacle apparatus of an 
unknown filter-feeding organism (Lindstrom, 1964), while still another (Foss, i960) 
has suggested that the similarity of their carbonate fluorapatite composition to that 
of scales of the Ordovician chordate Astraspis implies an affinity between the two. 



BRITISH AVONIAN CONODONT FAUNAS 5 

Studies of amino acid content and of ultramicroscopic structure of conodonts at 
present in progress may provide important new information on their affinities 
(Schwab, 1966 ; Armstrong & Tarlo, 1966). 

In spite of the uncertainty concerning their nature and function, studies on cono- 
dont successions during the last decade have shown conodonts to be one of the most 
sensitive and useful fossil groups available for stratigraphic correlation. Recent 
work by German palaeontologists (see p. 8 for detailed references) on the conodont 
faunas of the type sections of the Upper Devonian and Lower Carboniferous has 
provided the means of making even more precise regional correlation than those 
recognized by goniatites upon which " standard " correlations have been established 
(see, for example, Ziegler 1962). Furthermore, a broadly similar zonal sequence of 
conodonts has been established in the Mississippi Valley. 

The purpose of the present paper is to describe conodont faunas from the 
" Lower " Carboniferous rocks of the type section in the Avon Gorge, Bristol, from 
various parts of South Wales, and from Shropshire, Yorkshire and Scotland. Over 
600 samples from these areas have been processed, and have yielded over 25,000 
identifiable specimens. The sequence of the conodont faunas at present described 
provides the basis for a conodont zonation, which not only assists intra- and inter- 
basinal correlation in Britain, but also allows the first precise correlation with North 
America and Continental Europe. 

II. HISTORY OF PREVIOUS RESEARCH 
(a) History of previous conodont research in Britain 

Conodonts were first described by Pander (1856) and, although they were reported 
shortly afterwards from several localities in Britain, comparatively little attention 
has been paid to them in this country. 

Walliser (1958) recorded the oldest known stratigraphic occurrence in Britain, 
when he discovered a " paraconodont " from the Upper Cambrian Comley Limestone 
of Shropshire. 

Ordovician conodont faunas from Britain have been described from the Arenigian 
of the Southern Uplands (Smith 1907 ; Lamont & Lindstrom 1957) ; the Llan- 
deilian Llandeilo Limestone of Carmarthenshire (Rhodes 1953), and Castell Lime- 
stone of Pembrokeshire (Bergstrom 1964) ; the Upper Llandeilian and Lower 
Caradocian of the Southern Uplands ; the Caradocian wilsoni Shales of the Southern 
Uplands (Lindstrom 1957), Gelligrin, Pen-y-garnedd, Crug and Bryn Pig Limestones 
of Wales (Rhodes 1953 : Lindstrom 1959 : Bergstrom 1964) and the Ashgillian 
Keisley Limestone of Westmorland (Rhodes 1955) and Birdshill Limestone of 
Carmarthenshire (Bergstrom 1964). 

A number of early workers, including Harley (1861), Moore (1864), Young (1880A) 
and Smith & Jones (1881), recorded conodonts from Silurian rocks in Britain. 

A basal Llandovery fauna referable to the celloni Zone of Walliser (1964) from the 
Malverns was described by Brooks & Druce (1965). Llandoverian conodonts have 
also been noted by Whittard (1927) from the Pentamerus Beds of Shropshire and by 
Squirrell & Tucker (i960) from the Upper Llandoverian of the Woolhope Inlier. 



6 BRITISH AYONIAN CONODONT FAUNAS 

WenLockian conodonts have been collected from the Welsh Borderland by Hill (1936) 
and systematically described from Usk by Austin & Bassett (1967). Conodonts 
from the Woolhope, Wenlock, Aymestry and Whitclifhan Limestones of the Welsh 
Borderland were reported by Ireland (1958, 1962). Rhodes (1953) with Newall 
(1963) systematically described a fauna from the Aymestry Limestone of Shropshire 
and South Staffordshire. Squirrell & Tucker (i960) listed Upper Ludlovian cono- 
donts from the Woolhope Inlier and Collinson & Druce (1966) systematically 
described a fauna from the Whitcliffe Flags of Shropshire which was referable to the 
eosteinhomensis Zone of Walliser (1964). 

Dineley & Rhodes (1956) described Devonian conodonts from the Upper Givetian 
at Torquay, from the Lower Frasnian near Chudleigh, from the Lower Frasnian at 
East Ogwell and from the Lower Pilton Beds (Strunian) at Saunton, North Devon. 
They also described (1957) an Upper Devonian fauna from the limestones of the 
Bishopsteignton borehole. Matthews (1962) reported a late Eifelian fauna from a 
Middle Devonian limestone at Neal Point in the Tamar Valley. House (1963, table 
2) and House & Selwood (1964) have summarised known Devonian conodont 
occurrences in South West England. The only new conodont record noted by House 
& Selwood was an Upper Givetian conodont fauna from the Marble Cliff Beds, 
identified by Rhodes. Rhodes also identified Lower Givetian conodonts from the 
Middle Gramscatho Limestones for Hendriks (1966). Other limestones yielding 
Siegenian, Emsian and Middle Devonian conodonts are also mentioned. Ziegler 
(Hendriks 1966) has also extracted Frasnian conodonts from limestones interstitial 
with the Mullion Island pillow lavas. 

British Lower Carboniferous conodont studies have been few and brief. Moore 
(1863, 1870) listed conodonts from the Carboniferous Limestone of Yorkshire and 
Cumberland, Fowler (1955) mentioned conodonts obtained from a borehole in South- 
East County Tyrone, Eire, and Robbie (1955) reported conodonts from the Rossmore 
and Edenbrook beds of Lower Carboniferous age obtained from the subsurface at 
Edenork, County Tyrone, Ireland. Dineley & Rhodes (1956) studied eight samples 
from the Tournaisian of South West England. Small faunas from the Shirehampton 
Beds, the Lower Limestone Shale, the Black Rock Limestone, the Fish Bed and 
Horizon y, collected in the Avon Gorge, Bristol, were described, as also were faunas 
from the ? Black Rock Limestones of Windsor Hill, Somerset and Waterlip Quarry, 
Somerset. Matthews (1961, 1966) has identified anchoralis faunas collected at 
Viverdon Down near Callington, and from the St. Mellion area of South West 
England. Varker (1967) has described conodonts referable to the genus Apatog- 
nathus from the Yoredales of Northern England. 

Young (1880, 1880A) mentioned the occurrence of Scottish Carboniferous Lime- 
stone conodonts, in addition to those of the Silurian and Devonian of England. 
Smith (1900) reported conodonts from the Carboniferous limestones of Western 
Scotland and figured those described by Hinde (1879, 1900). These were sub- 
sequently refigured and redescribed by Clarke (i960) who also described faunas from 
the Scottish Carboniferous Limestone Series. Craig (1952, 1954) reported conodonts 
from the Top Hosie Shale, of Lower Carboniferous age, near Kilsyth, Scotland. 



BRITISH AVONIAN CONODONT FAUNAS 7 

Namurian conodonts were found in a borehole in a Yoredale type of deposit in the 
Cleveland Hills by Fowler (1944). Dunham & Stubblefield (1945) noted the 
occurrence of a platform conodont in the Colsterdale Marine Beds of the Millstone 
Grit of Yorkshire. Conodonts have also been noted in the Millstone Grit of the 
Midlands by Stevenson & Mitchell (1955). The only published systematic des- 
cription of British Namurian conodonts is that by Higgins (1961) who described a 
fauna from the Namurian of North Staffordshire. Collinson & Druce {in press) have 
described a conodont fauna from the lower boundary of the Namurian in County 
Clare, Eire. 

There have been no detailed systematic descriptions of British Pennsylvanian 
conodonts, but many workers have noted the presence of conodonts in the British 
Coal Measures. In Scotland, Currie, Duncan & Muir-Wood (1937) described 
conodonts from Skipsey's Marine Band, and the Upper Coal Measures in Central and 
West Scotland. Manson (1957) listed conodonts from a marine band in the Anthra- 
conaia modiolaris Zone of Scotland. Smith (1907A) recorded conodonts from the 
Upper Coal Measures (above the Craigmore Ironstone). 

Stevenson & Mitchell (1955), Stubblefield & Calver (1955), Mitchell (1954) and 
Eden (1954) reported conodonts from the Midland Coalfields, as also have Mitchell & 
Stubblefield (1941) from the Leicestershire and South Derbyshire Coalfield, Mitchell, 
Stubblefield & Crookall (1942, 1945) from the Warwickshire and northern part of the 
South Staffordshire Coalfields, Edwards & Stubblefield (1948) from the Derbyshire 
and Nottinghamshire Coalfields, and Edwards (1954) from the Clown Marine Band 
in Derbyshire and Nottinghamshire. Earp & Magraw (1955) listed conodonts from 
the Tonge's Marine Band in the Lower Coal Measures of Lancashire, and Magraw 
(1957) recorded conodonts from various marine bands in Lancashire, Derbyshire and 
Yorkshire. Ramsbottom (1952) and Woodland, Archer, Evans & Calver (1957) 
noted the presence of conodonts in the South Wales Coal Measures. 

There has been no reference to the occurrence of post-Pennsylvanian conodonts in 
the British Isles. 



(b) Carboniferous conodont zonation and correlation 

Although the Upper Devonian and Lower Carboniferous rocks of West Germany, 
the latter of which provide the standard for Carboniferous correlation, are tradi- 
tionally correlated on the basis of their cephalopod faunas, recent studies by German 
palaeontologists on the conodont faunas have shown that the latter offer a new 
degree of precision in problems of regional correlation. The most notable contribu- 
tions in this field are those of Bischoff (1955, 1956, 1957), Bischoff & Ziegler (1956, 
1957), Bartenstein & Bischoff (1962), Boger (1962), Kronberg, Pilger, Scherp & 
Ziegler (i960), Meischner (1962), Sannemann (1955, 1955A), Voges (1959, i960), 
Walliser (1958, i960) and Ziegler (1958, 1959, 1962, 1962A, 1962B). These workers 
described conodonts, which were associated with the classic Devonian and Lower 
Carboniferous cephalopod zones in West Germany, and a detailed Devonian and 
Lower Carboniferous conodont faunal succession has thus been established. 



8 BRITISH AVONIAN CONODONT FAUNAS 

This conodont succession has been applied to rocks of Upper Devonian and 
Carboniferous age in other parts of Western Europe, notably by Dvorak & Freyer 
(1961), Helms (1959, 1961), and Muller (1959) in East Germany ; Flugel & Ziegler 
(1957) in Austria ; Lys & Serre (1958), Higgins (1962), Higgins, Wagner-Gentis & 
Wagner (1964) in Spain ; Lys & Serre (1957), Lys, Serre & Deroo (1957), Lys, Serre, 
Mauvier & Grekoff (1961) in France and the Sahara ; Boogaard (1963) in Portugal ; 
and by Serre & Lys (i960) and Conil, Lys & Mauvier (1964) in Belgium. 



Germany 

The zonation of the Lower Carboniferous in Germany is based chiefly on the work 
of Bischoff (1957) and Voges (1959). 

Bischoff (1957) studied the conodont faunas of the Wocklumeria, Gattendorfia, 
Pericyclus and Goniatites Stages of the Rhenoherzynicum. He subdivided the 
Pericychis Stage into two conodont subzones — the Siphonodella Subzone (Cull a-(3) 
and the anchor alis Subzone (Cull y). He also described the conodont faunas of the 
three goniatite zones of the Goniatites Stage. 

Voges (1959) described conodonts from the Lower Carboniferous Gattendorfia and 
Pericyclus Stages. He recognized three zones within the Gattendorfia Stage : the 
Gnathodus kockeli-Pseudopolygnathus dentilineatus Zone ; the Siphonodella- 
Pseudopolygnathus triangulus inaequalis Zone and the Siphonodella-Pseudopoly- 
gnathus triangulus triangulus Zone. Three zones were recognized by Voges within 
the Pericyclus Stage ; the Siphonodella crenulata Zone (Cull a), which was sub- 
divided into a lower and an upper subzone, the Scaliognathus anchoralis Zone (Cu 
II Py), and a Scaliognathus anchor alis-Gnathodus bilineatus " interregnum " (Cu 
II S). Voges thus gave a more detailed and refined zonation than Bischoff (1957) 
for the Gattendorfia and Pericyclus Stages, and also differed from Bischoff by extend- 
ing the Scaliognathus anchoralis Zone into Cu II (5 (Bischoff confined the anchoralis 
Zone to Cu II y). 

The German workers were thus the first to attempt a conodont zonation of the 
Lower Carboniferous. Whilst not detracting in the least from the excellent work of 
Bischoff and of Voges it is true to say that there are a number of deficiencies and gaps 
in our knowledge of German conodont faunas. The reasons for these gaps are twofold. 
Firstly the nature of the outcrops is such that it is impossible to collect from con- 
tinuous exposures. The different samples collected by both Voges and Bischoff are 
from widely separated areas. Secondly, the sediments are such that in any one 
locality not all horizons yield conodonts (e.g. Hangenberg Schiefer, and the cherts 
immediately beneath the " Erdbach Kalk "). There has also been a marked 
tendency for German conodont workers to give total stratigraphic ranges of species, 
rather than the exact distribution and abundance of individual species, although 
more recently, for example Kronberg, Pilger, Scherp & Ziegler (i960) and Ziegler 
(1963), these have been given. It is becoming increasingly apparent from conodont 
studies in other parts of the world that numbers of stratigraphic breaks exist in the 
German succession, even where these have not hitherto been suspected. 



BRITISH AVONIAN CONODONT FAUNAS 9 

The Franco-Belgian Province 

Studies of the Franco-Belgian Lower Carboniferous conodont faunas are com- 
paratively recent. Serre & Lys (i960) described the distribution of Tournaisian and 
Visean conodonts in the Avesnois, Boulonnais and Hainault regions of Northern 
France and Belgium, and Conil, Lys & Mauvier (1964) recorded the ranges of conodont 
species in the type formations of the Dinantian in the Franco-Belgian Province. 
More recently Bouckaert & Ziegler (1965) have published an account of the conodont 
faunas of the Famennian Stage in Belgium. 

Conodont studies in the Franco-Belgian Province are important because these 
sections have yielded the type specimens of many Lower Carboniferous cephalopods. 
Unfortunately, however, neither Serre & Lys nor Conil, Lys & Mauvier have system- 
atically described or illustrated their specimens, and they have given no exact 
distribution or abundance data for individual species. Thus the work at present is 
of limited value. Few correlations can be made, although one which can be made 
with a fair degree of certainty is based on the distribution of Scaliognathus anchor alis. 
This species is restricted to Tn3 b in the Franco-Belgian Province and to the Cu 
II p y horizon in Germany. This is important, because hitherto it has been con- 
sidered likely that the Tournaisian- Visean boundary in Germany should be drawn 
at the base of Cu II (3 y, based on the distribution of Pericyclus princeps. This is the 
zonal fossil for Cu II a in Germany and was first found and described from the Tn 3c 
of Belgium. If the conodont correlations based on anchor alis are accepted, they are 
at variance with the " well established " goniatite evidence, although the literature 
does not contain a single reference to Pericyclus princeps having ever been found in 
Germany. It is therefore a very dubious " zonal fossil ". 

The need for systematic descriptions and illustrations of the Franco-Belgian 
conodonts is thus urgent for it may provide the key for unravelling the German 
succession and for filling the gaps which are present in Germany. 

The United States 

Lower Carboniferous conodont research in North America began in the mid 
nineteen-thirties. Huddle (1934) described the conodont fauna of the New Albany 
Shale in Indiana and Branson & Mehl, working in Missouri, described the conodont 
faunas of the Bushberg Sandstone (1934A), of the "Lower Mississippian Formations" 
(1938A), of the Caney Formation (1940) and of the Keokuk Formation in Iowa and 
Missouri (1941A). E. R. Branson (1934) also described conodonts from the Hannibal 
Formation in Missouri. 

Cooper (1939) described conodonts from the Bushberg Hannibal strata in Okla- 
homa and later, with Sloss (1943), described a fauna from a Lower Mississippian 
black shale in Montana and Alberta. 

Mehl & Thomas (1947) described the conodont fauna of the Fern Glen Formation 
in Missouri, and Thomas (1949) described the faunas of Lower Mississippian age from 
the English River and Prospect Hill Siltstones of South East Iowa. 

Hass described Lower Carboniferous conodonts from the Arkansas Novaculite of 



io BRITISH AVONIAN CONODONT FAUNAS 

Arkansas (1956A), the Maury Shale of Tennessee (1956), the Barnett Formation 
(1953) and the Chappel Limestone of Texas (1959). 

Scott & Collinson (1961) described a fauna from the Louisiana Limestone and 
from the McCraney Limestone. 

Youngquist & Patterson (1949) described conodonts from the Prospect Hill Sand- 
stone of Iowa. The fauna of the Lower Mississippian Wassonville Dolomite of Iowa 
was described by Youngquist & Downs (1951). Youngquist, Miller & Downs (1950) 
described Burlington conodonts from Iowa. 

Rexroad (1957) described Chester conodonts from Illinois and later (1958) from the 
Glen Dean Formation. Rexroad & Clarke (i960) described Glen Dean conodonts 
from Kentucky, Virginia and West Virginia. Golconda Group conodonts were 
described by Rexroad & Jarrell (1961). Those of the Kinkaid Formation in Illinois 
were described by Rexroad & Burton (1961) and those of the Paoli and equivalent 
formations in Illinois by Rexroad & Liebe (1962). 

From the work of these and other workers, it became clear that conodonts were 
abundant in Mississippian rocks and were useful for correlation of strata. As a 
result, the Illinois State Geological Survey, in co-operation with the University of 
Texas, the State University of Iowa, Texas Technological College, the University of 
Houston, and the Indiana Geological Survey, conducted a programme of research in 
the Mississippi Valley. In 1962 Collinson, Scott & Rexroad published a paper in 
which they described 17 conodont biostratigraphic zones, which were present in the 
Mississippian rocks of the Mississippi Valley. The limits and characteristic species 
of each zone were described and they also attempted to correlate these zones with the 
conodont zones present in Germany. 

Subsequent workers have systematically described the faunas of the biostrati- 
graphic zones established in 1962. Thus Rexroad & Collinson (1963) not only 
described the conodonts of the St. Louis Formation, but also indicated, described 
and illustrated the species characteristic of the Taphrognathus varians-Apatognathus 
Assemblage Zone and of the Apatognathus ? geminus-Cavusgnathus Assemblage Zone. 

In the same way Rexroad & Scott (1964) when describing the conodont faunas of 
the Rockford Limestone and the lower part of the New Providence Shale of Indiana 
described and illustrated the conodont fauna characteristic of the Siphonodella 
isosticha-S. cooperi, Gnathodus semiglaber-Pseudopolygnathus multistriatus, Bactro- 
gnathus-Polygnathus communis and Bactrognathus-T aphrognathus Assemblage Zones. 
They also showed in tables the numerical distribution and stratigraphic ranges of 
specimens. 

Rexroad & Collinson (1965) provided the same data for the Taphrognathus varians- 
Apatognathus Assemblage Zone, when describing the conodonts of the Keokuk, 
Warsaw and Salem Formations of Illinois. 

Rexroad & Furnish (1964) referred their fauna from the Pella Formation of South- 
Central Iowa to the Gnathodus bilineatus-Cavusgnathus charactus Assemblage Zone of 
the Mississippi Valley, and to the St. Genevieve Limestone in particular. 

Rexroad & Nicoll (1965) described the faunas of the Menard Formation, which 
they referred to the Kladognathus-Cavusgnathus naviculus Zone, drawing the lower 



BRITISH AVONIAN CONODONT FAUNAS n 

limit of that zone at the base of the Menard. Klapper (1966) described Upper 
Devonian and Lower Mississippian faunas from Montana, Wyoming and South 
Dakota, and identified the local equivalents of the German Cu I and Cu II a faunas. 
These studies have provided a most useful basis for the correlation of our Avonian 
faunas with those of the Mississippi Valley. 

Australia 

Recent studies by Glenister & Crespin (1959), Glenister (i960), Jones & Druce 
(1966) and Glenister & Klapper (1966) have shown the similarity of European- 
North American Devonian and Lower Carboniferous conodont faunas to those of 
comparable age in Australia. 

III. STRATIGRAPHY 

(a) Introduction to the stratigraphy of the Carboniferous of Britain 

Rocks of Lower Carboniferous age form one of the most extensive outcrop belts in 
the geology of Britain but, in spite of their extensive outcrop, generally good expo- 
sure, and the wealth of study devoted to them, precise correlation is often difficult 
between basins, and sometimes also within them. The distribution and character 
of Lower Carboniferous rocks is so well known that it needs only the merest introduc- 
tion in a study such as this, as it has recently been reviewed by George (1958). 

Lower Carboniferous rocks were deposited on an archipelago-like basement (Fig. 
1) dominated by a landmass to the north-west, by a caledonoid-trending massif 
which extended from north-eastern Ireland into the Southern Uplands, by a stable 
block in north-eastern England, and a great, east-west landmass, stretching from 
Leinster through Central Wales into the Midlands of England. To the south of this 
landmass, the south-western Province of the Carboniferous represented a basin of 
more or less continuous deposition, which extended westwards into Ireland and was 
bounded by a landmass in south-western Cornwall. It was marked by the deposi- 
tion of two distinctive facies groups. In the south, the Culm facies of Devon and 
Cornwall and southern Ireland included dark argillaceous and sometimes calcareous 
shales and mudstones, containing a few thin, impure, dark limestones and cherts, as 
well as subordinate sandstones and grits. To the north of this facies, in Somerset, 
Gloucestershire and South Wales, there was deposited the " limestone facies," 
consisting mainly of grey or light-blue bioclastic limestones, with subordinate 
dolomites, oolites and argillaceous limestones. These rocks contain a rich fauna of 
brachiopods and corals, as well as crinoids, ostracods, foraminifera and algae. In 
some parts of the section there is developed a " lagoon " facies, characterized by 
drab grey, calcite-mudstones, with subordinate calcareous shales and oolitic rocks. 
Calcareous algae, ostracods, gastropods and pelecypods are the main fossils of this 
group, which is present in the Modiola phase of south-western England. Both the 
Culm facies and the bioclastic limestone facies extend westwards into southern 
Ireland. 

Northern England was separated from Southern England for at least part of 
Carboniferous times, by the combined St. George's Land-Midland Barrier. In the 



12 



BRITISH AVONIAN CONODONT FAUNAS 




Fig. i. Generalized palaeogeographic map of Britain during Early Carboniferous times, 
showing main depositional regimes, and localities described in the text. Based partly 
on George (1958) and Wills (1952). 






BRITISH AVONIAN CONODONT FAUNAS 13 

Central Province, lying to the north of this barrier, rocks of Yoredale facies were 
deposited. These include cyclothemic limestones, non-marine sandstones, shale, and 
coal sequences, with a fauna of corals, brachiopods, bivalves, occasional goniatites 
and non-marine plants. Bioclastic limestones and spectacular reefs also developed 
in various places in this region, such as the reef knolls of Derbyshire and the Craven 
Lowlands, and the larger sheet-like apron reefs of Southern Ireland. 

In the Northumbrian trough, lying to the north of the Central Province, as well as 
in the trough of the Midland Valley of Scotland, which was separated from it, a 
distinctive facies of the Cementstone type was developed, consisting of alternating 
thin argillaceous limestones, sandstones and grey-black shales. Fossils are rare and 
include fish, ostracods, inarticulate brachiopods and spirorbid worms. These rocks 
are overlain by sandstones, coal-bearing strata and limestones, the total Northum- 
brian section including some 7,000 ft. of strata. In the Midland Valley of Scotland, 
a broadly similar variety of rock types is found, although there is no detailed 
equivalence in age ; clastic deposits predominate there, and include the Oil Shales 
and the Calciferous Sandstones. There are also thick lavas in places. 

In north-western Ireland great thicknesses of deltaic strata were deposited, which 
pass southwards into limestone-shale and bioclastic limestones (George 1955). 

Rocks of Lower Carboniferous age present formidable problems of correlation and 
these arise largely from the rapid and almost continuous lithological and faunal 
changes which they display. The general problems of correlation have been 
reviewed by Rayner (1953) and by George (1952 and 1958). The first successful 
attempt to provide a palaeontological subdivision of the rocks of the South-West 
Province was that of Vaughan (1905) who proposed the now widely-applied coral- 
brachiopod system for the limestones of south western England. This was based 
upon exhaustive and meticulous collecting of faunas, especially from the Avon Gorge. 
Vaughan established his zonal scheme on the first appearance of particular genera 
and species, although the zones as interpreted today are partly assemblage zones, 
based on the occurrence of a number of species. To a varying extent the demarca- 
tion of Vaughan 's zones was influenced by the marked lithological changes which 
occur in the Avonian strata of south-western England (see p. 17). 

It was early recognized that Vaughan's zonal scheme was inapplicable to the 
different facies of northern England and in that area the work of Bisat (1924) on 
goniatites provided the basis for much of the present classification. 

Present views on the validity of these various zonal schemes are sharply divided. 
There is general agreement that, in the sense in which they were originally established 
by Vaughan, the coral-brachiopod zones can no longer be applied in detail, but some 
workers, especially Kellaway & Welch (1955), reject the whole zonal scheme which 
they represent. The detailed problems of correlation are discussed on p. 52. 

(b) The Avonian Succession 

The Avon Gorge, Bristol, has long been regarded as the type area for the British 
" Lower " Carboniferous. The base of the Lower Limestone Shale was selected by 
Buckland & Conybeare (1824) and by De la Beche (1846) as the base of the Lower 



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BRITISH AVONIAN CONODONT FAUNAS 



15 



Carboniferous. Although Vaughan (1905) established a series of coral-brachiopod 
zones for the succession, these were later found to be of only local value in correlation 
(see George 1952, 1958 for a critical review), so that other type sections have been 
recognized for other areas of Britain (e.g. Walker 1964). The accepted international 
type section for the Lower Carboniferous is that in West Germany. 

The rocks of the Avon Gorge comprise some 3,000 ft. of strata, consisting pre- 
dominantly of carbonates, but with subordinate shales and sandstones. Vaughan 
(1905) subdivided these into five faunal zones, four of which were divided into two 
subzones (Fig. 2). Vaughan pointed out that the Dinantian was approximately, but 
not exactly, equivalent to his Avonian, which he subdivided into the underlying 
Clevedonian (C, Z, K) and the Kidwellian (D and S Zones), rather than using the 
equivalent Tournaisian and Visean. Vaughan modified his classification in later 
publications (1906, 1915 : Dixon & Vaughan 1911, Reynolds & Vaughan 1911). 
The modifications involved the inclusion of the Modiola phase as the basal subzone 
of K (Km), the varying position of horizon y (included in Z in 1905 ; in C in 191 1 ; 
included as the major part of C in Burrington Combe in 1911), and the development 
of the Caninia Zone (1906, 1911). Other authors also proposed subsequent amend- 
ments, Dixey & Sibly (1918) subdividing the C Zone in South Wales, and Hudson & 
Dunnington (1945) placing the Caninia Oolite in the Upper C Zone. 

The present standard coral-brachiopod zonation of the Avonian (modified after 
George 1958) is as follows : 



6 DlBUNOPHYLLUM ZONE 



5 Seminula Zone 



4 Upper Caninia Zone 



3 Lower Caninia Zone 
2 Zaphrentis Zone 
1 Cleistopora Zone 



Symbols 
D 



C 2 S 



201 



Ci 

z 

K 



Vaughan (1905) Subzones 

D2 and Di. 

Vaughan (1905) " Main 

Seminula Zone " of Dixey 

& Sibly (1918). 

Dixey & Sibly (1918). 

This includes part of Vau- 

ghan's (1905) Syringothyris 

Zone and the overlying 

Lower Seminula Zone (Si). 

The lower limit of this zone 

is placed at the top of the 

Caninia Oolite. 

Dixey & Sibly (1918), with 

horizon y at the base. 

Vaughan (1905) Subzones 

Z2 and Z,\. 

M and K Zones of Vaughan 

(1905) and the K Zone of 

Sibly (1906). 



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BRITISH AVONIAN CONODONT FAUNAS 17 

In this succession, Zones 1-3 are generally regarded as Tournaisian, and Zones 
4-6 as Visean. 

Vaughan's general zonal scheme has been the subject of much subsequent criticism, 
partly because of the extent to which the distribution of corals and brachiopods is 
influenced by environment, and partly also because of the lack of precision in 
defining boundaries. The K Zone, for example, was coincident with the lithological 
limits of the Lower Limestone Shale, its only fossil of any possible diagnostic value 
being Avonia bassus (George 1952). The faunas of other zones were no less reflec- 
tions of the facies changes represented by successive strata, the zaphrentid corals 
being but one example. In other areas, zonal fossil genera were found beyond the 
limits of these zones. 

It was for these reasons that Kellaway & Welch (1955) suggested the replacement 
of Vaughan's zones by a succession of lithological units (Fig. 3). The object of these 
was to assist in regional mapping, but such lithological units are of less value in 
correlation than Vaughan's imperfect faunal zones. Even Kellaway & Welch, 
whose divisions generally correspond with the limits of Vaughan's faunal zones, 
found lateral transition within this area, the Shirehampton Beds of Bristol passing 
southwards into the base of the Lower Limestone Shale, and northwards and 
westwards into the top of the Portishead Beds. 

Vaughan's faunal assemblage zones, defined by twin zonal indices, but strength- 
ened and supplemented by other index fossils, still seem to us to represent the most 
satisfactory method of correlation in the field, although we believe that the conodont 
zonation presented in the present paper provides a far more precise alternative for 
those strata in which conodonts are present. 

(c) Previous research on the correlation of the Avonian with the Carboniferous of Europe 

The correlation of the British Avonian with the continental succession has 
presented acute problems. Vaughan (1915) attempted to use the coral-brachiopod 
faunas to correlate with the Belgian succession. He correlated the Lower Tour- 
naisian (Ti) with his Z Zone and the Upper Tournaisian (T 2 ) with his C Zone 
(including the y horizon), making detailed correlations within the various units. He 
suggested that the faunal overlap (the Sublaevis Beds and the Marbre Noir Series) 
between the Visean and Tournaisian in the Dinantian succession was equivalent to 
the Upper C2 and Si Zones, and the Visean succession above V ia up to and including 
V 2cx to the S Zone. He correlated the Lower V 2c Beds with the Di, and the Upper 
V 2c with the D 2 of the Avon Gorge. Vaughan correlated the Hastiere Limestone 
and Shale, the " Octoplicata " Shale, and the base of the Landelies Limestone with 
his (3 horizon, but Paul (1937), on the basis of brachiopod faunas, suggested the 
equivalence of the upper part of Ki and of K 2 in the Avon Gorge with the Hastiere 
Limestone (Tn lb ). He regarded the Hastiere Limestone and the Per acuta Shale 
(Tn 2a ) as equivalent to the Gattendorfia Hangenberg Limestone of Germany, but 
Goldring (1958) suggested from their trilobite faunas that both these formations may 
be equivalent to the Lower Limestone Shale (Ki and K 2 ), and he correlated the base 
of the Black Rock Limestone (Zi) with the base of the Landelies Limestone (Tn 2b ). 



18 BRITISH AVONIAN CONODONT FAUNAS 

The outstanding difficulty of detailed correlation of the Avonian with the Car- 
boniferous type sections of the Rheinisches Schiefergebirge has been the absence of 
goniatites in the type Avonian section. A prolecanitid (Protocanites) (identified by 
Professor Frank Hodson) from shales near Abergavenny may have been collected 
from the lithologically similar shales at the top of the Z Zone or from the K Zone. 
The exact locality is not specified on the specimen, which is in the Geological Survey 
Collections (No. G.S.M. 82817) (see also George 1952 : 35). George & Howell (1939) 
have described Prolecanites discoides, Muensteroceras inconstans, and Pericyclus kochi 
from the Upper Caninia Oolite of Three Cliffs Bay, Gower, and these suggest an 
uppermost Tournaisian age for these beds, while the presence of Muensteroceras 
euryomphalus and Merocanites cf. compressus in the overlying Upper Caninia Beds 
suggest a low Visean age (George & Ponsford, 1935). The traditional Lower-Upper 
Avonian boundary (Dixon & Vaughan, 1912) of the Lower Caninia Zone (Ci) and 
Upper Caninia Zone (C2S1) is thus approximately equivalent to that of the Tour- 
naisian and Vis6an (see George 1952, 1955). Smith (1942 : 338) recorded a goniatite 
indicative of a P2 age from the Avonian Tanhouse Beds (D 3 ) of the Yate district in 
Gloucestershire. 

Currie (1954) provided a monographic study of Scottish Carboniferous goniatites 
which allowed her to make correlations with the stages established by Bisat. She 
was able to assign the Upper Limestone Group to the E2 (Arnsbergian) Stage, the 
Limestone Coal Group to the Ei (Pendleian), both the latter being of Lower 
Namurian age, the Lower Limestone Group to the P2 and the Upper and higher part 
of the Lower Oil Shale Group of the Calciferous Sandstone 'Series' to the Pi and B 
Stages (Bollandian and Cracoean) of the Middle and Upper Visean. Bisat's B2, Pi 
and P2 goniatite zones are equivalent to Vaughan's Dibunophyllum Zone, and his 
Bi Zone to the main Seminula Zone. Prentice & Thomas (1965 : 43, Fig. 2) have 
given a distribution table of British prolecanitids in which they show a correlation of 
Vaughan's D-C Zones in North Devon with the European goniatite zones, although 
they provide no detailed discussion of the broader aspects of correlation. 

In spite of these various studies, Lower Carboniferous correlations between Britain 
and continental Europe remain tenuous, the uncertainties arising chiefly from the 
absence of the more stratigraphically useful faunal groups common to the two areas. 
We believe that the closely comparable conodont faunas here described allow a far 
more refined correlation than any yet achieved. 

(d) The stratigraphy of areas from which conodonts are described 
(i). The Avon Gorge, Bristol. 

The Avon Gorge, Bristol, is the type area for the British Avonian. A series of 
steep, river-side cliffs, provide almost continuous exposures of rocks from the upper- 
most Old Red Sandstones at the base, to the highest beds of the D Zone of the 
Carboniferous at the top. 

The lowest beds of the Avonian section are thinly-bedded, grey, brown, green and 
red, marly claystones, thin grits, sandstones and fissile, slightly calcareous shales. 
There are few calcareous deposits, the first limestone occurring 12 ft. above the base 



BRITISH AVONIAN CONODONT FAUNAS 



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20 BRITISH AVONIAN CONODONT FAUNAS 

of the section. In the lower portion of the section fossils are rare, ostracods, gastro- 
pods and algae being the most common ; brachiopods and bivalves are generally 
rare. Ascending the sequence, fine grained compact limestones become more 
prominent, their upper bedding surfaces being covered with brachiopods and 
crinoids. The upper part of the Lower Cleistopora Beds is an alternating sequence of 
claystones and thin limestones, which has a banded appearance. Occasional more 
massive limestone bands, about one foot thick, are also interbedded. 

The highest beds of the shallow-water phase consist of seven distinct beds, 
separated by thin shale partings. The lower six beds range from n inches to z\ feet 
in thickness and are crinoidal limestones, which have been stained by haematite. 
The uppermost bed (the Bryozoa Bed) is a massive, limestone bed, eight feet thick, 
crowded with crinoids, bryozoa and small gastropods. 

The Upper Cleistopora Zone consists at the base of sandy fossiliferous limestones 
with interbedded calcareous shales. Near the base is a " gritty " six inch bed of 
crinoidal limestone, the Palate Bed, which contains bryozoa, palatal teeth and 
coprolites. Thinly bedded limestones, and alternating shales follow. The upper- 
most beds of the K Zone consist of blue-grey calcarenite beds, up to one and a half 
feet thick, and alternating brown silty shales. 

Horizon (3 consists of thinly bedded, coarse crinoidal limestone, with thin shale 
layers developed between the more massive limestone bands. The beds of the main 
Z Zone are blue-grey fossiliferous massive limestones, with some alternating, thinly- 
bedded limestones and a few shale partings. The limestones approach a " petit 
granit " in character. 

The Laminosa Dolomites were probably originally identical to the Z Beds in 
lithology, but subsequent dolomitisation has resulted in these beds weathering to a 
brownish colour, which contrasts strongly with the blue-grey limestones of the 
Zaphrentis Zone beneath and with the white oolites of the Caninia Zone above. 

The Caninia Oolite is a pinkish-grey, white-weathering, current-bedded, fine 
grained oolite with uniformly rounded grains. It is succeeded by a series of current- 
bedded, marly limestones, dolomitic limestones, occasional oolitic bands and blue, 
grey, yellow, green or red shales — the Caninia Dolomites and Shales. The uppermost 
beds of this group are more massive than the lower and less shale is developed in them. 

Shales and thick bands of dolomite with occasional oolites form the lowest beds of 
the Seminula Zone. They are essentially similar in lithology to the underlying 
Caninia Dolomites. They are followed by massive blue-grey limestones, which are 
frequently dolomitised, and by thin shales, which are succeeded in turn by calcite 
mudstones, which weather white. The shales become less conspicuous higher in the 
section, where grey Lithostrotion-bearing limestones predominate. The upper beds 
of the Seminula Zone, the S2 Subzone, consist of oolites and pisolites at the base and 
the Concretionary Beds at the top. The latter are fine-grained, argillaceous lime- 
stones, the upper surfaces of which are undulating. They are underlain by black 
shales, which ramify into the overlying limestone bands. The Concretionary Beds, 
which sometimes contain algae and ostracods, are interbedded with chinastones and 
occasional oolitic limestones. 



BRITISH AVONIAN CONODONT FAUNAS 21 

Massive grey foraminifera-bearing limestones, which are oolitic in places, form the 
lower beds of the T>i Subzone of the Dibunophyllum Zone. A few pseudobreccias 
are also developed. The Upper Di Beds consist of coarse oolites, alternating with 
thin shales and grits. In the D2 Subzone the lowest beds show an alternation of 
grits, limestones and shales. Higher in the section there are grey oolitic limestones, 
which contain foraminifera, crinoids and corals. The highest beds of the section 
consist of shales and grits, which are heavily stained with haematite. 

The section was sampled at ten-foot intervals, Vaughan's (1906) zonation and 
description being used as a basis for the collecting. The section sampled was sub- 
divided into nine traverses (Fig. 5). These were as follows : — 

1. The riverside traverse of the K Zone. Leigh Woods side of the Gorge. (ST 
556 746). 

Sample numbers K1-K17. 

2. The top of the K Zone and the basal 30' of Zi Quarry 1. Leigh Woods side of 
the Gorge. (ST 557 745). 

Samples K18-K21 and Z1-Z10. 

3. The Zi Limestone traverse in Black Rock Quarry. Clifton side of the Gorge. 
(ST 561 747). 

Sample numbers Z11-Z20. 



N 



74- 



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m 



Press Qi 



CLIFTON DOWN 



O 30 


3 YARDS 


SCALE 


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Fig. 5. Sketch map of the Avon Gorge, Bristol, showing localities mentioned in the text. 



22 BRITISH AVONIAN CONODONT FAUNAS 

4. The Z2 Limestone traverse in Quarry 2. Leigh Woods side of the Gorge. 
(ST 558 745)- 

Sample numbers Z21-Z38. 

5. The Laminosa Dolomite traverse in the Railway cutting, Leigh Woods side of 
the Gorge, between Quarry 2 and Quarry 3. (ST 559 745). 

Sample numbers Ci-Cii. 

6. The Laminosa Dolomite and Caninia Oolite traverse in Quarry 3. Leigh 
Woods side of the Gorge. (ST 560 744). 

Sample numbers C12-C25. 

7. The Caninia Dolomite traverse along the roadside on the Clifton side of the 
Gorge, between the Caninia Oolite Quarry to the North and the Great Quarry to 
the South. (ST 562 746). 

Sample numbers C26-C48. 

8. The Si and lower S2 traverse in the Great Quarry on the Clifton side of the 
Gorge. (ST 563 740). 

Sample numbers S1-S30. 

9. The S2 and Concretionary Bed riverside traverse, south of Quarry 4. Leigh 
Woods side of the Gorge. (ST 562 737). 

Sample numbers S31-S72. 

10. The D Zone traverse at the roadside, north of and a short distance to the 
south of Bridge Valley Road on the Clifton side of the Gorge. (ST 564 734). 
Sample numbers D1-D27. 



(ii) South Wales 

Rocks of Lower Carboniferous age form an extensive rim around the margins of the 
South Wales Coalfield, where they overstep the Old Red Sandstone. The thickest 
and most complete sequence is developed on the southern margin of the Coalfield in 
Pembrokeshire, Gower and the Vale of Glamorgan. The application of Vaughan's 
zonal scheme has shown that in this area the complete succession is present, the total 
thickness being in excess of 4,000 ft. in parts of Pembrokeshire and some 3,500 ft. in 
Gower, but thinning gradually eastwards. There is a broadly comparable litho- 
logical sequence to that of the Bristol area, comprising a lower limestone and shale 
sequence, followed by bioclastic limestones and oolites, but including varying 
developments of shales and pseudobreccias in the highest parts, and dolomites in the 
C and Z Zones in the east. On the North Crop of the coalfield the thickness is much 
reduced, however, partly as a result of original depositional thinning against the 
margins of a northerly landmass, partly because of intra-Avonian unconformities, 
and partly because of truncation below the transgressive unconformable base of the 
overlying Millstone Grit. The intra-Avonian unconformity cuts out much of the C 
and S Zones in places. 

Our collections were made chiefly from the North Crop of the Coalfield, though 



BRITISH AVONIAN CONODONT FAUNAS 



23 



smaller collections were also made from Gower and Pembrokeshire. Detailed 
descriptions of the local stratigraphy have been given by George (1927 and 1954), 
Dixey & Sibly (1918) and Owen & Jones (1955). Pringle & George (1961) have 
reviewed the regional stratigraphy. 

Detailed localities and measured sections are given in Figs 59-92 (p. 246), and 
it is necessary here to give only a brief introduction to the local succession. The 
youngest strata of the Avonian, the D 3 Upper Dibunophyllum Zone, or Upper 
Limestone Shale, are often cut out by Namurian overstep. The succession was 
collected by us at Mellte Bridge, at the confluence of the Rivers Mellte and Sychryd, 
near Craig-y-Dinas (SN 911079 : see Owen & Jones 1955) where it consists of 23 ft. 
of dark shales and interbedded muddy, and rarely crystalline, crinoidal limestones, 
most of them less than a foot in thickness. The samples yielded over 3,900 identifi- 
able specimens, whereas beds of similar age from the Black Lias Quarry at The 
Mumbles, Glamorgan (SS 615883) proved virtually barren in conodonts. 

The underlying D2 Beds were first collected from exposures in the valley of the 
River Nedd (SN 912122) but these proved to be unfossiliferous, and further collec- 
tions were made from Craig-y-Dinas (SN 911099) where some 64 ft. of strata are 
exposed. These consist of massive crystalline limestones with thin interbedded 
shales. Near the top of the section a thin irregular band of rolled fish framents and 
conodonts occurs. The samples yielded over 130 specimens. 




ABERGAVENNY 



Fig. 6. Map of South Wales to show the main outcrop of the Carboniferous Limestone. 



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BRITISH AVONIAN CONODONT FAUNAS 25 

These beds overlie some 80 ft. of massive crystalline limestones, which are assigned 
to the Di Subzone. Near the top a " honeycomb " is developed. These samples 
yielded no conodonts, and the underlying 300 ft. of S2 grey crystalline limestone 
also proved barren. 

The S2 and C2S1 Zones were collected at Llanelli Quarry (SO 223125), the S2 
comprising over 300 ft. of dolomitic, sandy, massive bedded limestones with occasional 
brachiopod lenses. The C2S1 section consists of about 50 ft. of porcellanous, compact 
calcite-mudstones with some oolites and green shales (George 1954). None of the 
samples from these exposures yielded conodonts. 

The underlying Z Zone was collected at Blackrock (SO 2 13 125) and consists of 
190 ft. of alternating oolites and sugary dolomites, with occasional thin shale bands. 
All samples in this section yielded conodonts, although some samples yielded only 
unidentifiable fragments. Over 5,000 specimens were recovered. 

The K Zone was collected in the banks of the River Clydach (SO 224126) and along 
the Heads of the Valleys Road (SO 225130), the contacts with the underlying red 
sandstone, referred to the Devonian, and the overlying Z Zone both being exposed. 
The unit consists of alternating calcarenite and shale bands, which range in thickness 
from 40 ft. to six inches. The limestone samples all yielded conodonts but the shales 
were unproductive. 

(iii) Shropshire 

Rocks of Lower Carboniferous age are rare in Shropshire, most of which was 
emergent during early Carboniferous times. Strata of Lower Carboniferous age, 
which outcrop on the northern and southern flanks of Titterstone Clee Hill, are also 
found at Little Wenlock and Lilleshall. Our collections were made at Farlow (SO 
642808), on the northern slopes of Titterstone Clee Hill, where conglomerates and 
overlying limestones and shales of the K Zone are well exposed. The basal con- 
glomerate, which reaches a thickness of some 40 ft. in places (Ball & Dineley 1961), 
overlies Grey Farlow Sandstones of the Upper Old Red Sandstone. The K Zone is 
overlain by Z Zone oolitic limestones, which are well exposed at Oreton (SO 648806). 
The overlying Cornbrook Sandstone, once regarded as representing the Caninia Zone, 
has been shown by Jones & Owen (1961) to be of Westphalian age. In contrast, the 
youngest Lower Carboniferous strata of the Little Wenlock area represent the 
Dibunophyllum Zone. 

The Z Zone was collected at Oreton Quarry (SO 648806) where it consists of 20 ft. 
of pale cream calcarenite, which yielded abundant conodonts. 

The underlying K Zone was collected in Farlow Lane (SO 642808), the contact 
between the zones being unexposed. The K Zone consists of alternating shales and 
limestones ; the lower shales contain quartz pebbles, and lie directly above con- 
glomerates referred to the Old Red Sandstone (Farlovian). Conodonts were 
recovered from all samples. 

(iv) Yorkshire 
The Yoredale Formation (Yoredale Series of Phillips 1836) is a succession of 



26 BRITISH AVONIAN CONODONT FAUNAS 

cyclothems typically developed in north-eastern England. In the type area on the 
Askrigg Block it overlies the Great Scar Limestone and is overlain by the Millstone 
Grit. The upper contact is partly conformable, partly unconformable ; the lower 
contact is an interdigitation. The typical cyclothem of the Yoredale Formation 
comprises a thick marine limestone overlain by shale, which is in turn succeeded 
by sandstone (Moore 1958, Walker 1964). The limestones resemble those of the 
Great Scar Limestone and the southward failure of the shales and sandstones results 
in a diachronous (interdigitating) contact between the Yoredale Formation and the 
Great Scar Limestone, obliterating at least three cyclothems. In Northumberland 
and Durham the interdigitation occurs at lower and lower levels within the Great 
Scar Limestone (here called the Melmerby Scar Limestone). The top of the Yoredale 
Formation extends higher than on the Askrigg Block in consequence of the occur- 
rence of limestones and the non-occurrence of the typical coarse pebbly sandstones 
of the Millstone Grit, in the generally cyclothemic sequence. In terms of the 
goniatite zones, the Yoredale Formation varies in age as follows : — 

Teesdale early B2 to R lb 

Wensleydale (= Yoredale) late B 2 to E lb 

Grassington P lc only 

The succession in the type area of the Yoredale Formation in Upper Wensleydale 
is complex, the major cyclothems between two successive thick limestones often 
including minor rhythms, which possess characters of the typical rhythmic unit, 
except for the persistence of the limestone (Phillips 1836, Moore 1958, Walker 1964). 
The succession (Moore 1958 : 94) is as follows : — 

IX Main Limestone 
VIII Underset Limestone 
VII Three Yard Limestone 
VI B 
VIA 
VI Five Yard Limestone 

V A 
V Middle Limestone 
IV C 
IV B 
IV A 
IV Simonstone Limestone 
III C 
IIIB 
III A 
III Hardraw Scar Limestone 
II Gayle Limestone 
I Hawes Limestone 
Names have not been applied to the thin impersistent limestones, which are 
designated by an index number, indicating the major cyclothem to which they belong, 
and by an index letter, showing their position in the cyclothem. 



BRITISH AVONIAN CONODONT FAUNAS 27 

Moore (1958 : 95) described the major limestone at the base of the cyclothems and 
grouped the other beds of the cyclothems together under the term " Non-Calcareous 
Measures" (although they sometimes contain thin limestones and calcareous shales). 

The lower boundary of the Yoredale Formation in the type area was placed by 
Moore at the base of a thin sandstone-shale sequence, the Thorny Force Sandstone, 
which lies below the Hawes Limestone. As pointed out by Walker (1964 : 210) 
this lowest cyclothem is poorly exposed and is confined to a small geographical area. 
The Girvanella Bed, which is accepted as the Di-D 2 boundary and hence roughly as 
the B2-Pi a boundary of the goniatite sequence, in the middle of the Hawes Lime- 
stone, is in this study taken as the base of the Yoredale Formation. 

The Hawes Limestone, which is forty feet thick, may be divided into two distinct 
members, a lower group of pale grey massive limestones, with pseudobreccias and a 
fauna of compound corals, and an upper group of blue-grey thinly bedded limestones 
with few fossils. The boundary between the two is the Girvanella Bed, which 
lithologically is part of the upper group. 

The Gayle Limestone, fifty-seven feet thick, may be divided into three parts. At 
the base is a group of wavy-bedded limestones with irregular shale partings. A 
massive bed, comparable in thickness to the whole of the underlying thin beds, forms 
the middle group. The upper part of the Gayle Limestone consists of massively- 
bedded, blue-grey, poorly-fossiliferous limestones. 

The Hardraw Scar Limestone, twenty-five feet thick, consists in the lower half of 
massive crinoidal limestones, often six feet thick at the base, which pass upwards 
into thinly-bedded, calcite mudstones. The upper part of the Hardraw Scar Lime- 
stone is more uniform than the lower, consisting of massive crinoidal limestones with 
partings of rubbly limestone, which pass up into finer-grained limestones and fine- 
grained calcite mudstones, which are partially dolomitised. 

Limestone III A is a fine-grained limestone containing corals (Lithostrotion) . 
Limestone III B is arenaceous and almost unfossiliferous, whereas Limestone III C 
is less sandy and contains small crinoids. 

The Simonstone Limestone, which is fifteen feet thick, consists in the lower part of 
a clastic limestone phase, with the development of coarse crinoidal limestones and 
sandy limestones with a sporadic fauna at the base, which passes upwards into a fine 
grained limestone and calcareous shale fades which often contains compound corals. 
The upper part of the Simonstone Limestone consists of fine grained limestone at the 
base, overlain in turn by coarsely crinoidal limestones and fine grained algal lime- 
stones. 

Limestone IV A, three feet thick, is a fine grained limestone, which is sandy at the 
base. Limestone IV B is a fine grained argillaceous limestone, z\ feet thick, with a 
9" bed of shale in the middle. 

The Middle Limestone, 65 feet thick, is divisible into three thick limestone units, 
each separated by shales and thin limestone bands. 

The Five Yard Limestone, two feet thick, consists of fine grained limestones, 
sparingly crinoidal, but with a rich fauna of corals and brachiopods. This formation 



28 



BRITISH AVONIAN CONODONT FAUNAS 



is usually developed in two beds with a parting of calcareous shale which has an 
abundant fauna. 

The Three Yard Limestone, which is eight feet thick, is a crinoidal fine grained 
limestone. 

Walker (1964 : 210) suggested that since a continuously exposed section through 
the whole Yoredale Formation did not exist in the type area, two sections, one 
representing the upper part and the other the lower part of the Formation, should be 
taken as type sections. Although Walker's section exposes the beds of his redefined 
Yoredale Series, it does not include the lower beds of the Yoredale Formation (as 
defined by Moore 1958). Walker described the upper part of the Formation, from 
the base of the Hardraw Scar Limestone to the top of the Underset Limestone, as 
exposed in Long Sike and North Scar Gill at the head of Snaizeholme Valley 
(SD/815840) which is west of the town of Hawes. The lower part of the Formation, 
from the base of the Hawes Limestone to the base of the Hardraw Scar Limestone, 
outcrops 3^ miles towards the north east in Gayle Beck (SD/864883), which is near the 
town of Hawes. The Hardraw Scar Limestone, according to Walker, forms a topo- 
graphic feature, which can be traced from the base of the first section to the top of the 
second, and this establishes the relative stratigraphic position of the two sections. 

In order to apply the conodont zonation established in south west England to 
northern England, fifteen samples, one or more being taken from each of the main 
limestones at the above localities, were processed. 




Fig. 8. Outline map of the Wensleydale area, North Yorkshire, from which the Yoredale 
succession was collected. 






BRITISH AVONIAN CONODONT FAUNAS 



29 



(v) Scotland 

Rocks of Carboniferous age outcrop over much of the Midland Valley of Scotland. 
Strata of " Lower " Carboniferous age lie below the Passage Group and Productive 
Coal Measures of the typical coalfield areas, but in places both the Passage Group and 
the Oil Shale Groups are replaced by contemporaneous lavas, chiefly of olivine 
basaltic composition. 

These strata were traditionally subdivided into two broad lithological series, 
the Calciferous Sandstone Series and an overlying Carboniferous Limestone 
Series. The lower of these divisions is now termed the Calciferous Sandstone 
Measures, and the upper division is no longer used on maps of the Geological Survey 
(MacGregor i960). The lowest division of the Calciferous Sandstone Measures, the 
Cementstone Group, consists of alternating fine-grained dolomite and shales, whilst 
the overlying Lower and Upper Shale Groups consist of alternating series of sand- 
stones, shales, coals, fireclays and limestones. Both marine and fresh-water lime- 
stones occur and oil shales are widespread . The greatest thickness of the Groups is 
in the East Fife Coalfield where some 4,000 ft. of strata occur. 

The overlying strata (the " Carboniferous Limestone Series " of earlier authors) 
are subdivided into three lithological groups, the Lower Limestone Group, the Lime- 
stone Coal Group, and the Upper Limestone Group. The two higher groups each 
have a maximum thickness of some 1,500 ft. in the West Fife Coalfield, while the 
maximum thickness of the Lower Limestone Group is only some 700 ft. Like the 
Calciferous Sandstone Measures, the whole Carboniferous Limestone " Series " thins 
rapidly southwestwards into the North Ayrshire Coalfield, where it is reduced in 
places to less than 100 ft. The Lower Limestone Group consists of thin marine 




Fig. 9. Outline map of Southern Scotland, showing localities mentioned in the text. 



30 BRITISH AVONIAN CONODONT FAUNAS 

limestones, including the Hosie Limestones, and inter-bedded shales, with sub- 
ordinate ironstone nodules and coals. Alternating sandstones, shales, fireclays, and 
workable coals and ironstones mark the Limestone Coal Group, while the Upper 
Limestone Group consists predominantly of sandstone, with subordinate shales, 
limestones and coals. 

I. Dunbar. Samples were collected from limestone bands within the Lower 
Limestone Group near Catcraig (NT 715772). The beds collected were the Long 
Craig Upper (NT 749752), Skateraw Lower (NT 748752), Skateraw Middle (NT 
743754), Skateraw Upper (NT 738758), Chapel Point (NT 722774), Barness East 
(NT 724773) and the Dryburn Foot (NT 732763) Limestones. 

II. Midlothian. The Lower Limestone Group was collected from various points 
in the Midlothian Coalfield. The " Gilmerton " Limestone was collected i| miles 
S.S.E. of Carlops (NT 172544) where it consists of grey crystalline limestone and 
shales, with a limestone breccia at the top. The North Greens Limestone was 
collected in Bilston Burn (NT 270649) and in the banks of the River North Esk, 
250 yds. S.W. of Newhall House. It consists of about 35 ft. of impure, thinly- 
bedded, argillaceous limestone. 

The Vexhim Limestones were collected in Glencorse Burn, 350 yds. upstream from 
Milston Bridge (NT 250628). 

The overlying Bilston Burn Limestone was collected in Bilston Burn, where it 
consists of about 40 ft. of thinly-bedded limestone, with an overlying bed of cal- 
careous shale and a 5 ft. bed of dolomitic limestone. 

III. Fife. A thick succession of the Calciferous Sandstone Measures and the 
Lower Limestone Group is exposed (Figs 85, 86) near Pittenweem (NO 548027) on 
the shore of the Firth of Forth, between Anstruther and Coal Farm. Samples 
were collected from the limestone and shale beds, the limestones yielding abundant 
conodonts, whereas the Calciferous Sandstone Measures, apart from three beds 
( x 5» 43' 3^8), were barren. 

IV. Ayrshire. Sections through the Lower Limestone Group and the Upper 
Limestone Group were collected. 

The Broadstone Limestone was collected at Auchenmade (NS 342486) where it is 
overlain by the Dockra Limestone, which was also collected here. The Hosie Lime- 
stones were collected in a railway cutting at Glengarnock (NS 333525). 

In the Upper Limestone Group the Index Limestone was collected near Glonbeith 
Castle (NS 332458) and near Drumbuie House (NS 361506) where it was about six 
feet thick. 

The Lower and Upper Linn Limestones were collected at the Linn Spout near 
Dairy (NS 287487, NS 284485). 

V. Roxburghshire. The Main Algal ' Series ' of Garwood (1931) was collected in 
Harden Burn (NY 517907) and the limestone bands, apart from the algal bed, 
yielded abundant conodonts. 

VI. Argyll. The Carboniferous Limestone 'Series' at Machrihanish (McCallien 
1928 ; McCallien & Anderson 1930) was examined and the limestones were collected 
where they were exposed on the beach (NR 632208). 



BRITISH AVONIAN CONODONT FAUNAS 31 

The general geology of the Scottish collecting areas is described in the following 
publications : Carruthers et al. (1927), Clough et al. (1925), Craig (1965), Currie 
(1954), Dinham & Holdane (1932), Goodlet (1957), George (1958), Mitchell & 
Mykura (1962), Richey et al. (1930), Robertson et al. (1949) and Tulloch & Walton 
(1958). 

IV. METHODS OF STUDY 

Samples were collected from the successions at intervals of 10 ft. and in many 
parts of the sections these were supplemented by collections made at 5 ft. or 2 ft. 
intervals. Most of the original samples from the reconnaissance survey weighed 
about 25 lbs. but the samples from the smaller intervals weighed only 2-4 lbs. 

These samples were weighed and then digested in 8% commercial acetic acid, 
contained in plastic buckets. Shales were disintegrated with concentrated hydro- 
gen peroxide, and formic acid was used for some of the limestones. After the rock 
had dissolved, the sludge was sieved under water on 25, 50, 100 and 200 mesh 
screens, the fractions being dried and then separated in bromoform. 

The heavy residues were searched with a binocular microscope and the conodonts 
picked and mounted (see Collinson 1963 for further details). 

Photography was carried out by Mr. S. Osborn, using a Leitz Aristophot apparatus 
and Adox KB 14 film, developed in Acutol or I.D. 48 developer. The specimens 
were coated with ammonium chloride. Prints were cut out and mounted but no 
retouching was undertaken. 

V. CONODONT FAUNAS 

(a) General Review 

The present study is based upon 600 rock samples, and has involved the solution of 
some 3 tons of rock, which yielded over 25,000 identifiable conodonts. We regard 
this total collection as satisfactory, although the average abundance of conodonts 
per kilogram of rock is considerably lower than the yields from some other areas. 

The distribution of conodonts within the various sections studied was far from 
uniform, and abundance ratios for each sample are included with each of the litho- 
logical sections (Figs 59-92). The succession in the Avon Gorge illustrates the 
problems involved in the less fossiliferous parts of the section. The average number 
of conodonts per kilogram was 8 for the K Zone, with a range from 0-47 per kilogram. 
In general the shales provided poor yields or were barren, while intervening lime- 
stones were relatively fossiliferous. Shale samples 7 and 8, for example, were barren, 
but they are separated by two thin limestones, yielding 20 and 16 conodonts per 
kilogram. 

The Z Zone consists predominantly of massive, blue-grey calcarenite, and has an 
average yield of 19 conodonts per kilogram. There is again a fair range of variation 
(0-66 per kg.), the lowest yields being in limestones with a high haematite content. 
The upper beds of the Zone had high yields (45-66 per kg.). 

In contrast, the Lower Ci, the Laminosa Dolomite, yielded an average of only 3 
conodonts per kilogram, probably reflecting either the destructive results of second- 



32 BRITISH AVONIAN CONODONT FAUNAS 

ary dolomitisation, or possibly an unfavourable depositional environment, while the 
upper Ci Caninia Oolite had an average yield of only i conodont per kilogram (range 
0-3 per kg.). Other conodont students have commonly found lithologically similar 
oolites to have low yields, and this may be the result of relatively rapid deposition. 
Of the 23 samples of the Caninia Dolomite which were processed, only one, a shelly 
calcarenite, yielded conodonts. 

S Zone samples had a yield of less than 1 per kilogram, and almost three quarters 
of the 72 samples processed were barren. Only 5 samples yielded an average of more 
than one conodont per kilogram. The Zone is marked by relatively little change in 
the conodont faunas, and, like the low yielding (1 per kg.) D Zone beds, probably 
represents rapidly deposited sediments. 

Broadly comparable variations in abundance are seen in strata of similar litho- 
logies from other sections. In the D Zone of South Wales, for example, the mean 
yield was 29 conodonts per kilogram of limestone dissolved, with a range from 0-198. 
In the Z Zone of the North Crop, the mean yield was 9 conodonts per kilogram, with 
a range from 0-60. In general the lowest yields were those of the saccharoidal 
dolomites, and the highest were those of the basal beds of oolites. 

(b) Stratigraphical distribution of conodont faunas 

The precise ranges of all conodont species recovered for each of the various areas 
are shown on Figs. 49-58. The present section provides only a general view of 
the distribution of some of the more useful genera and species. 

Patrognathus gen. nov. is restricted to the K Zone. The genus Clydagnathus gen. 
nov. is found in the K Zone and in the lower part of the Z Zone of the North Crop and 
in Shropshire. It is rare in large faunas of the same age from the Avon Gorge, 
although it occurs abundantly in some other countries, e.g. Australia. The lowest 
occurrence of the genus is represented by the species C. gilwernensis gen. et sp. nov. 
and C. cavusformis gen. et sp. nov., which are rapidly replaced by Clydagnathus sp. A 
gen. et sp. nov. The Lower Z Zone species are C. unicornis gen. et sp. nov. and C. 
darensis gen. et sp. nov. The genus Siphonodella, which has proved to be abundant 
and of great stratigraphical value in other areas, is rare in the Avonian. It is con- 
fined to the upper part of the K Zone in both the Avon Gorge and the North Crop. 
The limited stratigraphic range of the genus in the Avonian is also reflected in an 
absence of the sequence of species, which has been described from the Mississippi 
Valley. 

The genus Pseudopolygnathus is one of the most distinctive components of the 
faunas of the K and Z Zones, extending from the base of the K Zone into the Ci 
Laminosa Dolomite. It is represented by a considerable number of species, most of 
which have restricted stratigraphical ranges. Pseudopolygnathus vogesi sp. nov. and 
Pseudopolygnathus expansus sp. nov. are confined to the lowest part of the K Zone, 
where they are distinctive species. The Z Zone is characterized by the incoming of 
abundant pseudopolygnathids, referable to the species P. primus Branson & Mehl 
and P. cf. dentilineatus E. R. Branson. These are replaced vertically by P. postino- 
dosus sp. nov. and P. nodomarginatus E. R. Branson. In contrast to the abundance 



BRITISH AVONIAN CONODONT FAUNAS 



33 



Feet 
180 



160- 



140 



120 



100- 



40- 



20- 



100 



60 



60- 



20- 



Distribution and relative abundance of species of 
S patho g nathodus and related genera. 



Pseudopolygnathus sp. 



I 



S.tndentatus S.crassidentatus 



S.costatus - , , 
sulciferus S.costatusss. 



I 



S.plumulus ss 



Clydagnathus 
cavusensis 



S.plumulus 
nodosus 



Pseudopolygnathus 
vogesi 



Splumulu 
shirleyoel 



S.elongatus 



S.anteposicorni! 



Scf. robust us 



Scyrius 



I „ ( 



Percenta g e of 
total conodont 
fauna 

0-1 °/o 

1-5°/o 
5-15"».J 
15-30°/« 

>30°/o| 



Fig. io. Distribution and relative abundance of species of Spathognathodus and related 
genera in the Z and K Zones of the Avonian of the North Crop. 



34 BRITISH AVONIAN CONODONT FAUNAS 

of Pseudopolygnathus in the Lower Z Zone of the Avon Gorge, the genus is absent in 
strata of similar age from the North Crop. In these latter faunas it is presumably 
represented by functional homoeomorphs in the natural conodont assemblages. 
These could well be spathognathodids, from which Pseudopolygnathus seems to have 
arisen. The Lower Z Zone assemblage is replaced by abundant P. multistriatus Mehl 
& Thomas near the base of the Z2 Subzone, which is in turn replaced by abundant 
P. longiposticus (Branson & Mehl) towards the top of the Z2 Subzone. The genus is 
rare in the Lower Ci Subzone. 

The genus Gnathodus is one of the longest ranging in the Avonian, but its restricted 
and distinctive species have been particularly useful in some of our correlations. Its 
oldest occurrence is near the base of the Z2 Subzone, where G. delicatus Branson & 
Mehl is found. On the North Crop, G. simplicatus sp. nov. also occurs in Lower Z 
Zone faunas. G. delicatus is associated near the top of the Z2 Subzone with G. semi- 
glaber (Bischoff), a distinctive Upper Z Zone species, which is in turn replaced by G. 
antetexanus Rexroad & Scott at the top of the Z Zone. G. punctatus (Cooper), G. 
avonensis sp. nov. and G. simplicatus sp. nov. also occur in the Upper Z Zone. A 
single specimen of G. cuneiformis Mehl & Thomas was collected in the middle of the 
Si Subzone. Gnathodus is rare or absent in the higher C and S faunas, but is 
represented by several distinctive species in the D Zone. G. bilineatus (Roundy) 
appears at the base of the D2 Subzone, together with G. girtyi girtyi Hass. In the 
highest part of the D2 Subzone G. girtyi simplex Dunn, G. commutatus (Branson & 
Mehl), G. mononodosus sp. nov. and G. homopunctatus Ziegler appear. G. girtyi 
collinsoni sub. sp. nov. appears in the middle of the D 3 Subzone, and G. girtyi 
turritus Collinson & Druce near the top (Fig. 11). 

The genus Spathognathodus has an extended range, being present throughout the 
Avonian. The dominant species of the Lower K Zone is S. plumulus sp. nov., which 
is represented by several subspecies. The Upper K Zone is marked by a variety of 
spathognathodids, including S. elongatus (Branson & Mehl), Spathognathodus cf. 
robustus (Branson & Mehl), 5. anteposicornis Scott, and 5. tridentatus (E. R. Branson). 
The three former species, though never abundant, extend into the Lower Z Zone, 
while the latter, together with S. crassidentatus, which first appears in the basal K 
Zone, is abundant in the Lower and Middle Z Zone. S. costatus costatus (E. R. 
Branson) and S. costatus sulciferus (Branson & Mehl) appear in the Lower Z Zone in 
the North Crop and are abundant in the middle part of the Zone. S. cyrius (Cooper), 
a rare species throughout the K and Lower Z Zones, overlaps the lower occurrence of 
these species, and S. cf. cristulus Youngquist & Miller is also present, extending 
upwards into the C Zone. S. pulcher Branson & Mehl occurs high in the Z Zone and 
5. coronus sp. nov. in the C Zone. S. scitulus (Hinde) is present in the Caninia 
Oolite and extends into the D Zone. S. cristulus Youngquist & Miller is character- 
istic of the D2 Subzone and S. campbelli Rexroad of the D3. 

Polygnathus first appears near the base of the K Zone and extends to the top of Ci. 
Polygnathus communis Branson & Mehl extends from near the base of the K Zone to 
the middle of the Laminosa Dolomite. Polygnathus inornatus inornatus Branson & 
Mehl, P. lobatus lobatus Branson & Mehl, P. inornatus rostratus subsp. nov., P. 






RANGES OF IMPORTANT 
SPECIES OF CNATHODUS 




C 2 S, 



1 r 



No gnathodids 



BRITISH AVONIAN CONODONT FAUNAS 35 

inornatus vexatus subsp. nov. and P. lobatus inflexus subsp. nov. appear in the Middle 
K Zone. The P. inornatus group becomes extinct in the upper part of the K Zone. 
The P. lacinatus Huddle group appears in the uppermost Z Zone, together with P. 
lacinatus asymmetricus subsp. nov. The C Zone is characterized by P. lacinatus s.s. 
and P. bischoffi sp. nov. 

The genus Mestognathus first appears in the upper part of the Ci Subzone, where it 
is represented by M. beckmanni Bischoff, which extends into the D Zone. M . bipluti 
Higgins first appears in the Di Subzone and extends into the higher part of D2, where 
M. neddensis sp. nov. is also present. Neither extends into the D 3 Subzone. 

Cavusgnathus is most characteristic of the C2, S and D Zones. C. unicornis 
Youngquist & Miller is present in the C2 Caninia Dolomite and extends into the D 
Zone. C. charactus Rexroad first occurs in the C2S1 Zone, and C. convexus Rexroad 
is characteristic of the Middle S Zone. 

The genus Taphrognathus is restricted to the Upper S2 Subzone, where it is 
represented by a single species, T. varians Branson & Mehl. 

The striking genera Bactrognathus, Doliognathus, Scaliognathus and Staurognathus, 
which are distinctive components of faunas of comparable age in other areas, are 
unrepresented in our Avonian faunas, in which the genus Elictognathus is represented 
by only a single fractured specimen. It seems probable that these genera were 
geographically or ecologically restricted. 

Most of the genera of " bars and blades " have a long stratigraphic distribution, 
but a number of species have proved valuable in local correlation. Ligonodina beata 
nom. nov., Hindeodella corpulenta Branson & Mehl, and H. subtilis Ulrich & Bassler 
are common Upper K and Z Zone forms. Apatognathus makes its first appearance in 
the Z2 Subzone. A. geminus (Hinde) is present in the Ci Subzone and extends into 
the D Zone. A. scalenus Varker appears in the Upper Ci Subzone. A. bladus sp. 
nov. is confined to the D2 Subzone. Prioniodina laevipostica (Rexroad & Collinson) 
is limited to the Upper D2 Subzone. N eopHoniodus scitulus (Branson & Mehl), N. 
peracutus (Hinde), Hindeodella undata Branson & Mehl, and H. antecomplex Collinson 
& Druce first appear in the Lower D3 Subzone. Magnilaterella clarkei sp. nov. is 
confined to the D Zone, as is Kladognathus. 

The precise ranges of these and other species are given on Figs. 49-58. The low 
yield of conodonts from many samples makes reliance upon any single " index fossil " 
an unreliable method of correlation, but the general characteristics of the individual 
conodont assemblages are distinctive for each of our main stratigraphic divisions, 
and these provide the basis of a relatively precise scheme of correlation. 

(c) Avonian Conodont Biostratigraphical Zones 

A series of 14 conodont assemblage zones has been established. We have used the 
Avon Gorge and the North Crop successions as our type sections, using the latter to 
provide the three highest Avonian Zones, which are largely represented by non- 
carbonate sediments in the Avon Gorge area. We have therefore included in this 
section a detailed discussion of the correlation between these two areas, in order to 
provide a basis for the zonal scheme, which we have used (p. 46) to establish correla- 



36 



BRITISH AVONIAN CONODONT FAUNAS 



tions between these type sections and Avonian sequences in Central England and 
Scotland. We believe that these conodont zones provide a useful method of 
correlation throughout the British Avonian, and that they offer a considerably 
higher degree of precision than existing coral-brachiopod zones. 

They show no detailed correspondence to the conodont zones established in either 
the Mississippi Valley or in West Germany, although the general faunal sequence in 
the three areas has enough broad resemblances to allow us to correlate between them 
with some confidence. 

The sequence and relationship of the 14 zones are shown in Fig. 12. They 
are defined and described below, and the detailed correlation between the Avon 
Gorge and the North Crop is discussed. The intercontinental correlations given for 
each zone below are generalized and approximate. There is a full discussion of 
correlation on p. 52. 

Patrognathus variabilis — Spathognathodus plumulus Assemblage Zone 

Characteristic species : Patrognathus variabilis gen. et sp. nov., Spatho- 
gnathodus plumulus plumulus sp. nov., Pseudopolygnathus vogesi sp. nov., Spatho- 
gnathodus plumulus shirleyae sp. et subsp. nov. and, in North Crop, Clydagnathus 
gilwernensis gen. et sp. nov. 

Limits : The base of the assemblage zone is not identified, but probably corres- 
ponds to the first appearance of P. variabilis gen. et sp. nov. The upper limit 
coincides with the oldest stratigraphic occurrence of Polygnathus inornatus inornatus 
Branson & Mehl, Polygnathus lobatus lobatus Branson & Mehl, and also of the genus 
Siphonodella. 

Remarks : This zone occupies the lower and middle of the K Zone (Samples K 1- 
K 11 in the Avon Gorge and Samples KL i-KL 13 on the North Crop). It is 
correlated with part of the Cu I of West Germany, the lower and middle parts of the 
Hannibal Formation of North America and with the Tn2b and Lower Tn2 C of Belgium. 

The lowest Lower Limestone Shale, which immediately overlies the Old Red 
Sandstone in the Avon Gorge, does not contain conodonts. The basal limestone 
stratum (Sample K 3) is characterized by the presence of S. plumulus plumulus 
subsp. nov. and P. variabilis gen. et sp. nov. Sample K 4 is the oldest from the 
Avon Gorge to contain pseudopolygnathids, whereas these pseudopolygnathids 
occur in the North Crop in the basal beds of the Lower Limestone Shale which 
directly overlies the Old Red Sandstone. 



Fig. 13. Chart to show the characteristic species of the conodont zones proposed in the 
present paper. Where a species is shown breaking the boundary between two successive 
zones, it is present in both. 

Patrognathus variabilis — Spathognathodus plumulus Assemblage Zone. ia. Patrognathus 
variabilis gen. et sp. nov. — oral view. ib. Patrognathus variabilis gen. et sp. nov. — 
lateral view. 2a. Spathognathodus plumulus plumulus sp. nov. — lateral view. 2b. 
Spathognathodus plumulus plumulus sp. nov. — oral view. 3a. Pseudopolygnathus 
vogesi sp. nov. — oral view. 3b. Pseudopolygnathus vogesi sp. nov. — aboral view. 
4a. Spathognathodus plumulus shirleyae subsp. nov. — lateral view. 4b. Spathognathodus 



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:> i J 2i.fi.Lt ion Hi tlit Avoni.m nn the bails i.f .:..n.").>nts. shewing tlit relatiniiship ol the zones proposed in this paper to the cor;ii/brachiopod 
divisions ..I the Avon Gorjje, and tht North Crop, and also the relationship of the Yorcdalc strata in the upptr p.irt .if the succession. A 
comparison is made with the conodont zones established in the Mississippi Valley and wiih the Hematite /.one* of Europe. 



36 

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BRITISH AVONIAN CONODONT FAUNAS 37 

plumulus shirleyae subsp. nov. — oral view. 5a. Clydagnathus gilwernensis gen. et sp. 
nov. — oral view. 5b. Clydagnathus gilwernensis gen. et sp. nov. — lateral view. 

Siphonodella — Polygnathus inornatus Assemblage Zone. 6a. Polygnathus inornatus 
inornatus — lateral view. 6b. Polygnathus inornatus inornatus — oral view. 7a. Poly- 
gnathus lobatus lobatus — oral view. 8. Polygnathus lobatus inflexus — oral view. 9a. Poly- 
gnathus inornatus rostratus — oral view. 9b. Polygnathus inornatus rostratus — aboral view. 
10a. Siphonodella isosticha — aboral view. 10b. Siphonodella isosticha — oral view. 
Spathognathodus cf. robustus — S. tridentatus Assemblage Zone. n. Spathognathodus 
cf. robustus — lateral view. 12. Spathognathodus elongatus — lateral view. 13a. Spatho- 
gnathodus tridentatus — lateral view. 13b. Spathognathodus tridentatus — oral view. 
13c. Spathognathodus tridentatus — aboral view. 14. Spathognathodus crassidentatus — 
lateral view. 15. Spathognathodus anleposicornis — lateral view. 

Spathognathodus costatus costalus — Gnathodus delicatus Assemblage Zone. 16a. Spatho- 
gnathodus costatus costatus — lateral view. 16b. Spathognathodus costatus costatus — aboral 
view. 17a. Spathognathodus costatus sulciferus — lateral view. 17b. Spathognathodus 
costatus sulciferus — oral view. 18a. Spathognathodus cf. cristulus — lateral view. 
18b. Spathognathodus cf. cristulus — oral view. 19. Spathognathodus cf. cyrius — lateral 
view. 20a. Gnathodus delicatus — lateral view. 20b. Gnathodus delicatus — oral view. 
21. Ligonodina beata nom. nov. — inner lateral view. 22. Hindeodella corpulenta — lateral 
view. 23. Hindeodella subtilis — lateral view. 24a. Pseudopolygnathus primus — oral 
view. 24b. Pseudopolygnathus primus — aboral view. 25. Pseudopolygnathus cf. 
dentilineatus — oral view. 26a. Pseudopolygnathus multistriatus — aboral view. 26b. 
Pseudopolygnathus multistriatus — oral view. 27. Gnathodus simplicatus sp. nov. — oral 
view. 28a. Clydagnathus unicornis gen. et sp. nov. — oral view. 28b. Clydagnathus 
unicornis gen. et sp. nov. — lateral view. 29a. Pseudopolygnathus postinodosus sp. nov. — 
oral view. 29b. Pseudopolygnathus postinodosus sp. nov. — lateral view. 

Polygnathus lacinatus Assemblage Zone. 30. Polygnathus lacinatus lacinatus — oral 
view. 31a. Polygnathus lacinatus asymmetricus subsp. nov. — lateral view. 31b. Poly- 
gnathus lacinatus asymmetricus subsp. nov. — oral view. 32. Polygnathus nodomarginatus — 
oral view. 33a. Cavusgnathus sp. nov. A. — oral view. 33b. Cavusgnathus sp. nov. 
A. — lateral view. 34. Pseudopolygnathus multistriatus — oral view. 

Polygnathus lacinatus — Pseudopolygnathus cf. P. longiposticus Assemblage Zone. 
35. Gnathodus semiglaber — oral view. 36a. Gnathodus delicatus — lateral view. 36b. 
Gnathodus delicatus — oral view. 37. P. cf. longiposticus — lateral view. 38. Polygnathus 
lacinatus lacinatus — oral view. 39a. Spathognathodus pulcher — oral view. 39b. Spatho- 
gnathodus pulcher — lateral view. 40. Gnathodus simplicatus sp. nov. — oral view. 41a. 
Gnathodus avonensis sp. nov. — oral view. 41b. Gnathodus avonensis sp. nov. — lateral 
view. 

Gnathodus antetexanus — Polygnathus lacinatus Assemblage Zone. 42. Apatognathus 
geminus — inner lateral view. 43. Apatognathus scalenus — inner lateral view. 44. 
Apatognathus petilus — outer lateral view. 45a. Spathognathodus cf. cristulus — lateral 
view. 45b. Spathognathodus cf. cristulus — oral view. 46. Gnathodus antetexanus — oral 
view. 

Mestognathus beckmanni — Polygnathus bischoffi Assemblage Zone. 47a. Mestognathus 
beckmanni — lateral view. 47b. Mestognathus beckmanni — oral view. 48a. Polygnathus 
bischoffi sp. nov. — oral view. 48b. Polygnathus bischoffi sp. nov. — aboral view. 

Cavusgnathus unicornis — Apatognathus Assemblage Zone. 49. Cavusgnathus unicornis 
— inner lateral view. 50a. Spathognathodus cristulus — lateral view. 50b. Spathognatho- 
dus cristulus — oral view. 51a. Mestognathus beckmanni — inner lateral view. 51b. 
Mestognathus beckmanni — oral view. 52a. Gnathodus cuneiformis — oral view. 52b. 
Gnathodus cuneiformis — lateral view. 53a. Cavusgnathus charactus — oral view. 53b. 

[Caption to Fig. 13 continued on p. 38 



38 BRITISH AVONIAN CONODONT FAUNAS 

In addition, on the North Crop two subzones can be delineated, the lower being 
characterized by the presence of Spathognathodus plumulus nodosus sp. et subsp. nov., 
Clydagnathus gilwernensis gen. et sp. nov. and Psendopolygnathus vogesi sp. nov. 
The upper is recognized by the absence of the above-mentioned species and by the 
presence of Clydagnathus sp. nov. A. 

Siphonodella — Polygnathus inornatus Assemblage Zone 

Characteristic species : Polygnathus inornatus inornatus Branson & Mehl, 
Polygnathus lobatus lobatus Branson & Mehl, Polygnathus lobatus inflexus subsp. nov., 
Polygnathus inornatus rostratus subsp. nov. and Siphonodella isosticha (Cooper). 

Limits : The base of this zone is marked by the first occurrence of Siphonodella 
isosticha (Cooper), P. inornatus inornatus Branson & Mehl, P. lobatus lobatus Branson 
& Mehl, and P. inornatus rostratus subsp. nov. The top of the zone is marked by the 



Continuation of Fig. 13 caption] 

Cavusgnathus charactus — inner lateral view. 54a. Cavusgnathus cristatus — inner lateral 
view. 54b. Cavusgnathus cristatus — oral view. 

Taphrognathus varians — Cavusgnathus — Apatognathus Assemblage Zone. 55a. 
Taphrognathus varians — oral view. 55b. Taphrognathus varians — lateral view. 56a. 
Spathognathodus cristulus — oral view. 56b. Spathognathodus cristulus — lateral view. 

Apatognathus ? geminus — Cavusgnathus Assemblage Zone. 57a. Cavusgnathus 
cristatus — inner lateral view. 57b. Cavusgnathus cristatus — oral view. 58. Apato- 
gnathus ? geminus — inner lateral view. 

Mestognathus beckmanni — Gnathodus bilineatus Assemblage Zone. 59a. Mestognathus 
beckmanni — inner lateral view. 59b. Mestognathus beckmanni — oral view. 60. Cavus- 
gnathus unicornis — inner lateral view. 61. Spathognathus scitulus — lateral view. 
62a. Apatognathus bladus sp. nov. — inner lateral view. 62b. Apatognathus bladus sp. 
nov. — outer lateral view. 63. Hibbardella abnormis — inner lateral view. 64. Neo- 
prioniodus singularis — lateral view. 65a. Gnathodus girtyi girtyi — oral view. 65b. 
Gnathodus girtyi girtyi — lateral view. 66a. Gnathodus bilineatus — oral view. 66b. 
Gnathodus bilineatus — lateral view. 

Gnathodus mononodosus Assemblage Zone. 67a. Gnathodus girtyi simplex— lateral 
view. 67b. Gnathodus girtyi simplex — oral view. 68a. Gnathodus mononodosus sp. 
nov. — lateral view. 68b. Gnathodus mononodosus sp. nov. — oral view. 68c. Gnathodus 
mononodosus sp. nov. — aboral view. 69a. Gnathodus commutatus — lateral view. 69b. 
Gnathodus commutatus — oral view. 70a. Gnathodus homopunctatus — lateral view. 70b. 
Gnathodus homopunctatus — oral view. 71a. Spathognathodus cf. cristulus — lateral view. 
71b. Spathognathodus cf. cristulus — oral view. 

Gnathodus girtyi collinsoni Assemblage Zone. 72a. Gnathodus girtyi collinsoni subsp. 
nov. — oral view. 72b. Gnathodus girtyi collinsoni subsp. nov. — lateral view. 73a. 
Gnathodus girtyi simplex — oral view. 73b. Gnathodus girtyi simplex — lateral view. 
74a. Gnathodus girtyi girtyi — oral view. 74b. Gnathodus girtyi girtyi — lateral view. 
75a. Gnathodus nodosus — lateral view. 75b. Gnathodus nodosus — lateral view. 75c. 
Gnathodus nodosus — -aboral view. 76a. Gnathodus mononodosus sp. nov. — lateral view. 
76b. Gnathodus mononodosus sp. nov. — oral view. 76c. Gnathodus mononodosus sp. nov. — 
aboral view. 77a. Gnathodus bilineatus — oral view. 77b. Gnathodus bilineatus — lateral 
view. 78. Prioniodina stipans — lateral view. 79. Prioniodina subaequalis — lateral view. 
80. Neoprioniodus scitulus — lateral view. 81. Neoprioniodus tulensis — lateral view. 
82. Ligonodina levis — inner lateral view. 



BRITISH AVONIAN CONODONT FAUNAS 39 

first appearance of Spathognathodus cf. robustus (Branson & Mehl), S. tridentatus 
(E. R. Branson) and S. anteposicornis Scott. 

Remarks : This zone occupies nearly all the Upper K Zone in the North Crop 
and the lower part of the Upper K Zone in the Avon Gorge (Samples K 12-K2I in the 
Avon Gorge and Samples KL 16-KL 18 on the North Crop). It is correlated with 
the Upper Cu I and basal Cu II a of West Germany, the lower part of the Upper 
Hannibal Formation of North America and with part of the Tn2 C of Belgium. 

On the North Crop a covered shale interval is present between Samples KL 13 
and KL 16. In the Avon Gorge Samples K 12-K 17 contain P. variabilis gen. et sp. 
nov. and S. piumulus s.s. sp. nov., associated with the P. inornatus group. On the 
North Crop (Samples KL 16-KL 18) P. variabilis gen. et sp. nov. and S. piumulus s.s. 
sp. nov. are absent from the zone. 5. isosticha (Cooper) has not been found in the 
Avon Gorge, but there is a concealed interval above K 17 and below K2I. There 
are thus two subzones within this assemblage zone. The lower corresponds to 
Samples K 12-K 17 in the Avon Gorge and occupies the covered interval between 
KL 13 and KL 16 on the North Crop ; the upper subzone (KL 16-KL 18 of the 
North Crop) occupies the concealed interval above K 17 and below K2I in the 
Avon Gorge. 

Spathognathodus cf. robustus — Spathognathodus tridentatus 

Assemblage Zone 

Characteristic species : S. cf. robustus (Branson & Mehl), S. elongatus (Branson 
& Mehl), 5. tridentatus (E. R. Branson), S. crassidentatus (Branson & Mehl) and S. 
anteposicornis Scott. 

Limits : The base of this zone is marked by the first occurrence of Spathognathodus 
cf. robustus (Branson & Mehl), 5. tridentatus (E. R. Branson) and S. anteposicornis 
Scott. 

The top of the zone is marked by the first occurrence of Spathognathodus costatus 
costatus (E. R. Branson). The final appearance of the Polygnathus inornatus group 
is within the lower part of the zone. 

Remarks : This zone occupies the upper part of the Upper K Zone in the Avon 
Gorge (Sample K21) and the uppermost K and basal Z Zone on the North Crop 
(Samples KL 19-ZLA 1). It is correlated with the upper part of the Hannibal 
Formation of North America, with the Lower Cu II a of Germany and with the 
Upper Tn 2c of Belgium (see also p. 56). 

The lower part of this zone (with the P. inornatus group) probably occurs in the 
concealed interval beneath Sample K2I in the Avon Gorge. 

Spathognathodus costatus costatus — Gnathodus delicatus Assemblage Zone 

Characteristic species : In both the Avon Gorge and the North Crop : S. 
costatus costatus (E. R. Branson), S. costatus sulciferus (Branson & Mehl), 5. cf. 
cristulus Youngquist & Miller, S. cyrius (Cooper), 5. crassidentatus (Branson & Mehl), 
G delicatus Branson & Mehl, Ligonodina beata nom. nov., Hindeodella corpulenta 



4 o BRITISH AVONIAN CONODONT FAUNAS 

Branson & Mehl, Hindeodella subtilis Ulrich & Bassler. In the Avon Gorge : 
Pseudopolygnathus primus Branson & Mehl, Pseudopolygnathus cf . dentilineatus E. R. 
Branson, Pseudopolygnathus postinodosus sp. nov. On the North Crop : Clyda- 
gnathus unicornis gen. et sp. nov., and Gnathodus simplicatus sp. nov. 

Limits : The base of this assemblage zone is marked by the first occurrence of S. 
costatus costatus (E. R. Branson) and 5. cf. cristulus Youngquist & Miller. The top of 
the assemblage zone is recognized by the incoming of abundant Pseudopolygnathus 
multistriatus Mehl & Thomas and by the replacement of G. delicatus Branson & Mehl 
by G. semiglaber (Bischoff) and G. antetexanus Rexroad & Scott. 

Remarks : This zone occupies the uppermost K, the Zi and the lower part of the 
Z2 Subzones in the Avon Gorge and most of the Z Zone on the North Crop. (Avon 
Gorge Samples K 18-Z 25 : North Crop Samples ZLA 2-ZLA 28). It is correlated 
with the uppermost Hannibal, the Lower and Upper Chouteau Formation of North 
America, with the Middle and Upper Cu II a of Germany, and with the uppermost 
Tn2c and the Tn3 a of Belgium. 

This assemblage zone shows some geographical differences. Spathognathodus 
costatus costatus (E. R. Branson) first appears in the North Crop at the base of Sample 
ZLA 2, some distance within the Z Zone, and is quickly followed by S. costatus 
sulciferus (Branson & Mehl). In the Avon Gorge, on the other hand, these two 
species are present in the uppermost beds of the K Zone. It is believed that Pseudo- 
polygnathus primus Branson & Mehl evolved from S. costatus sulciferus Branson & 
Mehl. In the Avon Gorge at the base of the Z Zone there is a burst of pseudopoly- 
gnathids and the genus Pseudopolygnathus dominates the early Z Zone fauna. The 
genus Pseudopolygnathus is not present in the Lower Z Zone in the North Crop, its 
position in the natural conodont assemblages of the Z Zone on the North Crop being 
represented by other form genera. 

As a result, the following three subzones are recognized on the North Crop : 
C. Clydagnathus unicornis (Samples ZL 11-ZLA 28). 
B. Gnathodus simplicatus (Samples ZLA 15-ZL 10). 

A. Spathognathodus costatus costatus-Spathognathodus costatus sulciferus 
(Samples ZLA 2-ZLA 14). 

The base of the Spathognathodus costatus costatus-Spathognathodus costatus 
sulciferus Assemblage Subzone is marked by the first occurrence of S. costatus 
costatus (E. R. Branson) and 5. cf. cristulus Youngquist & Miller. The subzone is 
recognized by the presence of the above, together with S. costatus sulciferus (Branson 
& Mehl), Gnathodus delicatus Branson & Mehl, and Apatognathus varians Branson & 
Mehl. The Gnathodus simplicatus sp. nov. Assemblage Subzone is recognized by the 
first occurrence of Gnathodus simplicatus sp. nov. and the presence of Gnathodus sp. B. 
The top of this assemblage subzone is marked by the final occurrence of P. communis 
Branson & Mehl, N. barbatus (Branson & Mehl), 5. costatus sulciferus (Branson & 
Mehl) and A. varians (Branson & Mehl). The C. unicornis gen. et sp. nov. 
Assemblage Subzone is marked by the paucity of the conodont fauna. What 
fauna there is, is dominated by the presence of C. unicornis gen. et sp. nov., which up 
to this point has been extremely rare. The top of this subzone is marked by the 



BRITISH AVONIAN CONODONT FAUNAS 41 

disappearance of 5. tridentatus (E. R. Branson), Clydagnathus darensis gen. et sp. 
nov., C. unicornis gen. et sp. nov. and S. crassidentatus (Branson & Mehl). 

In the Avon Gorge there are two subzones : a lower subzone characterized by the 
presence of S. costatus costatus (E. R. Branson), 5. costatus sulciferus (Branson & 
Mehl) and S. cf. cristulus Youngquist & Miller, with very few pseudopolygnathids 
present, (Samples K 18-Z 9) and an upper zone of pseudopolygnathids (Samples 
Z 10-Z 25). In the subzone of abundant pseudopolygnathids, Pseudopolygnathus 
primus (Branson & Mehl) and Pseudopolygnathus cf. dentilineatus are abundant. 
Pseudopolygnathus multistriatus Mehl & Thomas has its lowest stratigraphic occur- 
rence in Sample Z 23. 

Polygnathus lacinatus Assemblage Zone 

Characteristic species : Polygnathus lacinatus s. s. Huddle, Polygnathus 
lacinatus asymmetricus subsp. nov., Pseudopolygnathus nodomarginatus (E. R. 
Branson), Spathognathodus pulcher Branson & Mehl and Pseudopolygnathus multi- 
striatus Mehl & Thomas. Gnathodus antetexanus Rexroad & Scott, is present near 
the base of the zone in the North Crop and at Farlow. 

Limits : The lower limit is marked by the incoming of the P. lacinatus group and 
of Gnathodus semiglaber (Bischoff). It is also a zone of abundant Pseudopolygnathus 
multistriatus Mehl & Thomas. The upper limit is marked by the incoming of 
Pseudopolygnathus cf. longiposticus (Branson & Mehl). 

Remarks : This zone occupies the uppermost part of the Z sequence in the North 
Crop and occurs near, but not at the top of, the Z Zone in the Avon Gorge, (North 
Crop Samples ZLA 29-ZL 19 : Avon Gorge Samples Z 26-Z 32). It is correlated 
with the unconformity at the base of the Sedalia Formation of North America, with 
the lowest Cu II (3-y of Germany and with the base of Tn3 b of Belgium. The 
presence of G. semiglaber and P. multistriatus in this zone indicates its broad equiv- 
alence to the Sedalia Formation, but the fact that it also contains abundant G. 
delicatus also implies a similarity to the underlying Upper Chouteau Formation. 
These two formations are separated by an unconformity in the Mississippi Valley, 
below which abundant G. delicatus occur, but above which this species is absent. It 
seems probable that beds Z 26-28, in which the two groups of species overlap, are 
broadly equivalent to the Chouteau-Sedalia unconformity time interval of the 
Mississippi Valley (see also p. 59). 

Polygnathus lacinatus — Pseudopolygnathus cf. longiposticus 

Assemblage Zone 

Characteristic species : G. semiglaber (Bischoff), G. delicatus Branson & Mehl, 
P. cf. longiposticus (Branson & Mehl), Polygnathus lacinatus s.s. Huddle, Spatho- 
gnathodus pulcher Branson & Mehl, Gnathodus simplicatus sp. nov. and Gnathodus 
avonensis sp. nov. 

Limits : The lower limit is marked by the lower limit of abundant P. cf. longi- 
posticus (Branson & Mehl). It is also a zone of abundant Gnathodus. The upper 



42 BRITISH AVONIAN CONODONT FAUNAS 

limit is marked by the disappearance of P. cf. longiposticus (Branson & Mehl) and by 
the replacement of G. semiglaber (Bischoff) by G. antetexanus Rexroad & Scott in the 
Avon Gorge. 

Remarks : This assemblage zone occupies the uppermost part of the Z Zone in 
the Avon Gorge (samples Z 33-Z 38). It is absent, owing to an unconformity, in the 
North Crop. It is correlated with the Fern Glen Formation of North America, the 
Middle Cu II (3-y of Germany, and the Tn3 b in Belgium. 

Gnathodus antetexanus — Polygnathus lacinatus Assemblage Zone 

Characteristic species : Polygnathus lacinatus s.s. Huddle, Apatognathus 
geminus (Hinde), Apatognathus scalenus (Varker), Apatognathus petilus Varker, S. cf. 
cristulus Youngquist & Miller and G. antetexanus Rexroad and Scott. 

Limits : The lower limit of the zone is marked by the youngest occurrence of P. 
cf . longiposticus (Branson & Mehl) . The lower limit of the genus Apatognathus in the 
Avon Gorge is near the lower limit of the zone. The upper limit of the zone is 
marked by the oldest stratigraphic occurrence of Mestognathus beckmanni Bischoff. 

Remarks : This zone occupies the lower part of the Ci Subzone in the Avon Gorge 
(Samples C i-C 14). It is not present on the North Crop. It is correlated with the 
lower, middle and lower upper parts of the Burlington Formation of North America, 
with the upper part of Tn3 b and possibly the lowest Tn3 C of Belgium and with the 
Upper Cu II (3-y of Germany. 

In this assemblage zone conodonts are sparse. The genus Pseudopolygnathus is 
represented by a considerably smaller number of specimens than in the underlying 
zone. Specimens of the P. lacinatus group, S. cf. cristulus Youngquist & Miller and 
A . scalenus (Varker) dominate the fauna. The youngest stratigraphic occurrence of 
P. communis communis Branson & Mehl in the Avon Gorge is within this zone. 

Mestognathus beckmanni — Polygnathus bischoffi Assemblage Zone 

Characteristic species : Mestognathus beckmanni Bischoff, 5. cf. cristulus 
Youngquist & Miller, Polygnathus bischoffi, sp. nov., A. scalenus Varker, A. petilus 
Varker, and A. geminus (Hinde). 

Limits : The lower limit of the zone is defined by the oldest stratigraphic 
occurrence of Mestognathus beckmanni. The upper limit probably coincides with 
the zone of maximum abundance of G. texanus (Roundy). 

Remarks : This assemblage zone occupies the upper part of the Ci Subzone in the 
Avon Gorge (Samples C 15-C 25). It is correlated with part of the Upper Burlington 
Formation of North America, with the lowest Cu II 8 of Germany and with part of 
the Tn3 C of Belgium. 

The upper limit of this assemblage zone cannot be defined in the Avon Gorge, 
because the lower beds of the Caninia Dolomite do not contain conodonts. 

The conodont fauna obtained from the Upper Avonian C2, Si, S2, and D Zones of 
the Avon Gorge is sparse in comparison with that obtained from the Lower Avonian. 



BRITISH AVONIAN CONODONT FAUNAS 43 

A gap is present in the conodont record of the lower part of the Caninia Dolomites 
(Samples C 26-C 28). Dr. S. C. Matthews (personal communication) has a small 
fauna of anchot ■alis-bilineatus interval aspect from an oolitic facies in the Mendips, 
which represents the lateral equivalent of the Caninia Dolomite. This fauna 
correlates with part of the Cu II S of Western Europe and with the Keokuk Formation 
of North America. 

Cavusgnathus unicornis — Apatognathus libratus Assemblage Zone 

Characteristic species : Apatognathus libratus Varker, Cavusgnathus unicornis 
Youngquist & Miller, 5. cristulus Youngquist & Miller, M. beckmanni Bischoff, 
Gnathodus cuneiformis Mehl & Thomas, Cavusgnathus charactus Rexroad, and 
Cavusgnathus cri status Branson & Mehl. 

Limits : The lowest occurrence of the zone in the Avon Gorge coincides with the 
oldest stratigraphic occurrence of Cavusgnathus unicornis Youngquist & Miller, 
although the true base of the assemblage zone cannot be accurately defined because 
of the absence of conodont faunas in the Caninia Dolomite. One sample (C 39) of 
the Caninia Dolomite has yielded a fauna containing C. unicornis Youngquist & 
Miller and M. beckmanni Bischoff. This indicates that at least the upper part of the 
Caninia Dolomite is within this assemblage zone. The upper limit of the assemblage 
zone coincides with the oldest stratigraphic occurrence of Taphrognathus varians 
Branson & Mehl, which is found in the Upper S2 Subzone. 

Remarks : This assemblage zone occupies the C2S1 Zone and the lower and 
middle of the S2 Subzone (Samples C 39-S 44). Together with the overlying 
Taphrognathus varians-Cavusgnathus- Apatognathus Assemblage Zone, it is equiva- 
lent to the middle and upper part of Cu II S in Europe and to the Warsaw, Salem, 
and lower part of the St. Louis Formation of North America. 

The very small number of conodonts present in this stratigraphic interval precludes 
a more detailed division, although the presence of G. cuneiformis Branson & Mehl at 
the base of the assemblage zone may provide the basis for future correlation. The 
overall aspect of the conodont faunas from this and the overlying conodont assembl- 
age zone of the Avonian are similar to those described by Rexroad & Collinson (1963 
and 1965) (see p. 61 for detailed discussion). 

Taphrognathus varians — Cavusgnathus — Apatognathus Assemblage Zone 

Characteristic species : T. varians Branson & Mehl, C. unicornis Youngquist 
& Miller, and S. cristulus Youngquist & Miller. 

Limits : The limits of this assemblage zone coincide with the stratigraphic range 
of T. varians Branson & Mehl as at present known in the Avonian. 

Remarks : This assemblage zone is present in the upper part of the S2 Subzone 
of the Avonian (Samples S 45-S 58). It is tentatively correlated with the lower part 
of the St. Louis Formation of North America. It is equivalent to the uppermost 
Cu II 8 in Germany. 

Specimens transitional between Cavusgnathus and Taphrognathus, which are 



44 BRITISH AYONIAN CONODONT FAUNAS 

identical to those from the St. Louis illustrated by Rexroad & Collinson (1963), have 
been found in this assemblage zone. 

Apatognathus geminus — Cavusgnathus Assemblage Zone 

Characteristic species : Cavusgnathus spp. and Apatognathus geminus (Hinde). 

Limits : The lower limit is marked by the last appearance of Taphrognathus 
varians Branson & Mehl. The upper limit of the zone is marked by the first appear- 
ance of Gnathodus bilineatus (Roundy). 

Remarks : This assemblage zone occupies the Upper S2 and the Di Subzones 
(Samples S 59-D 9) . No Di Subzone conodonts were recovered from the North Crop. 
The assemblage zone is one of few conodonts, but is characterized by the presence of 
the genera Apatognathus Branson & Mehl and Cavusgnathus Harris & Hollingsworth. 
It is tentatively correlated with the Apatognathus geminus-Cavusgnathus Assemblage 
Zone of North America, which is found in the upper part of the St. Louis Formation. 
This is equivalent to the lowest part of Cu III a in Germany. 

Sample D 10 which marks the first appearance of G. bilineatus (Roundy) is tenta- 
tively taken as the basal sample of D2 although the D1-D2 boundary in the type 
section is difficult to determine. One anomalous feature of this zone is the occurrence 
of a fauna from the North of England associated with Bollandoceras hodderense (Bi). 
This would generally be correlated with S2 of the Avonian (e.g. Thomas & Prentice 
1965 : 43). This fauna includes M. bipluti Higgins with G. symmutatus sp. nov., 
G. girtyi simplex Dunn, G. commutatus Branson & Mehl), G. bilineatus (Roundy) and 
G. homopunctatus Ziegler. 

The subsequent assemblage zones were established from the D2 and D3 successions 
on the North Crop. The few scattered conodonts of this age that were recovered 
from the Avon Gorge show a general similarity to the North Crop faunas. 

Mestognathus beckmanni — Gnathodus bilineatus Assemblage Zone 

Characteristic species : Mestognathus beckmanni Bischoff, Cavusgnathus 
unicornis Youngquist & Miller, Spathognathodus scitulus (Hinde), Apatognathus 
bladus sp. nov., Hibbardella abnormis Branson & Mehl, Neoprioniodus montanaensis 
(Scott), Gnathodus girtyi girtyi Hass, G. bilineatus (Roundy), and indeterminate 
magnilaterellids. 

Limits : The lower limit of the zone is tentatively taken as the first appearance 
of G. bilineatus (Roundy), but the absence of conodonts in samples of Di North Crop 
strata makes this position provisional. Further collecting will probably reveal an 
earlier occurrence of this species, which is present in Cu III a of Germany. The top 
of the zone is marked by the incoming of G. mononodosus sp. nov. 

Remarks : This assemblage zone is represented by the lowest 60 ft. of the D2 
Subzone of the North Crop (Samples CYD i-CYD 6). It is equivalent to part of the 
Cu III a in Germany, and broadly equivalent to the St. Genevieve Formation of the 
Mississippi Valley. The zone is no younger than the Pib Subzone of Northern 
England. 



BRITISH AVONIAN CONODONT FAUNAS 45 

Gnathodus mononodosus Assemblage Zone 

Characteristic species : Gnathodus girtyi simplex Dunn, G. girtyi girtyi Hass, 
G. mononodosus sp. nov., G. bilineatus (Roundy), G. commutatus (Branson & Mehl), 
G. homopunctatus Ziegler, and Spathognathodus cristulus Youngquist. Mestognathus 
neddensis sp. nov. and M. bipluti Higgins are characteristic of this zone in the North 
Crop. 

Limits : The lower limit is marked by the first appearance of G. mononodosus sp. 
nov. The upper limit is marked by the first appearance of Gnathodus girtyi collinsoni 
subsp. nov. The latter subspecies has not yet been recorded from the Midlothian 
section, however. 

Remarks : This zone is represented by the highest 10 ft. of the D2 Subzone and 
by the lowest 6 ft. of the D 3 Subzone (Samples CYD 7-3D 7) in the North Crop. 
Our Yoredale samples have yielded no mestognathids. No mestognathids are 
present in the Fife faunas and Collinson & Druce (in press) failed to recover them from 
their Irish Visean fauna. We agree with their suggestion that the genus has an 
irregular geographic distribution. It is not present in the prolific Upper Mississippi 
Valley faunas of this age. The top of this zone in the Yoredales is the top of the 
Simonstone Limestone (Pid). It is equivalent to the Cu III (3 of Germany and to 
the late Valmeyran of the Upper Mississippi Valley. 

Gnathodus girtyi collinsoni Assemblage Zone 

Characteristic species : Gnathodus girtyi collinsoni subsp. nov., G. girtyi 
simplex Dunn, G. girtyi girtyi Hass, G. nodosus Bischoff, G. mononodosus sp. nov., G. 
bilineatus (Roundy). Prioniodina stipans (Rexroad) and P. subaequalis (Higgins) 
are characteristic of the lower part of this zone in the North Crop and in Dunbar. 
Neoprioniodus scitulus (Branson & Mehl), N. tulensis (Pander) and Ligonodina levis 
(Branson & Mehl) are characteristic of the higher part in Scotland. 

Limits : The lower limit is marked by the first appearance of G. girtyi collinsoni 
subsp. nov. The upper limit is not defined in the present study. 

Remarks : This zone is represented by the uppermost 18 ft. of the D 3 Subzone 
of the North Crop (Samples 3D 8-3D 23). In the Yoredale section it is represented 
by samples Y 29-Y 10 comprising the Middle Pi d , the Five Yard, the Three Yard 
and the Underset Limestone (P2b-P2c)- The zone is equivalent to the Cu III y of 
Germany and broadly equivalent to the Lower Chesterian of the Mississippi Valley. 
It may be partly equivalent to the Lower Namurian, depending on where the upper 
boundary is ultimately defined. G. girtyi turritus Collinson & Druce is known to 
extend into the Namurian in Eire (Collinson & Druce in press). It is broadly 
equivalent to the pre-Middle Glen Dean Chesterian faunas of North America. 

The establishment of zonal limits in the upper part of the D succession was 
difficult. The last appearance of Mestognathus beckmanni, Mestognathus bipluti, 
Gnathodus homopunctatus, and the first appearance of Cavusgnathus naviculus, 
Gnathodus nodosus and Gnathodus girtyi turritus were each in turn considered as 



46 BRITISH AVONIAN CONODONT FAUNAS 

possible markers for zonal limits, but the first appearance of Gnathodus girtyi 
collinsoni subsp. nov. was the one in our opinion with the most widespread and 
meaningful application. 

Within a broad depositional basin there is a general similarity between the species 
of " bar and blade " conodonts in each of the upper zones, but these similarities do 
not extend to more distant areas, and we have therefore not listed them as character- 
istic of the zones as a whole. 



(d) Intra-Avonian correlation in Britain 

(i) Avon Gorge — North Crop (Figs. 49-52). 

There is a close overall similarity between the Lower K conodont faunas of both the 
Avon Gorge and the North Crop (Fig. 14). The lowest beds of both are characterized 
by the presence of Spathognathodus plumulus plumulus sp. et subsp. nov. and Patro- 
gnathus variabilis gen. et sp. nov. The absence in the lowest beds of the North Crop 
of Pseudopolygnathus vogesi sp. nov. which is present in the basal beds of the Avon 
Gorge, probably implies a slightly older age for the North Crop strata. Siphonodella, 
a most important diagnostic genus for the Carboniferous, and the Polygnathus 
inornatus group first appear at comparable horizons in the North Crop and the Avon 
Gorge. The last appearance of Siphonodella in both sections coincides with the first 
appearance of Spathognathodus robustus, a species whose first appearance overlaps 
the last appearance of the Polygnathus inornatus group. 

In the Avon Gorge, Spathognathodus costatus costatus first appears just below the 
traditionally accepted K-Z Zone boundary, whereas in the North Crop, it occurs just 
above it. The general ranges of all these species are so similar in the two areas, that 
correlation is relatively straightforward. Details are given on p. 36 in the zonal 
discussion and in Fig. 14. 

In spite of the overall lithological similarity between the Lower Z Zone strata in 
both areas, there is a lack of any detailed resemblance in their platform conodont 
faunas. We tentatively interpret this as the result of geographical isolation of 
certain conodontifers (see p. 36). This probably reflects the influence of palaeo- 
geographical factors, in spite of the fact that other studies have suggested a relatively 
uniform depositional basin in this area during early Z times. 

The incoming of Polygnathus lacinatus and of characteristic Pseudopolygnathus 
multistriatus in the higher part of the Z Zone of both areas provides a firm basis for 
correlation. The absence of Pseudopolygnathus cf. longiposticus in the North Crop 
suggests that the higher part of the Z Zone is unrepresented there. 

S2 and C2S1 rocks from the North Crop have yielded no conodonts, and Avon Gorge 
faunas of this general age and also of the Di Subzone are also sparse. The presence of 
Gnathodus bilineatus near the base of D2 in both areas re-establishes the correlation 
in the higher part of the Avonian. Above this level, conodonts are so rare in the 
Avon Gorge that no useful comparison can be made with the abundant faunas of 
the North Crop. 



BRITISH AVONIAN CONODONT FAUNAS 



47 



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48 BRITISH AVONIAN CONODONT FAUNAS 

(ii) Farlow (Fig. 53). 

The K Zone samples from Farlow (FAR 4A-7) yield a fauna broadly similar to that 
of the lower strata of the Avon Gorge, and the North Crop, although there are some 
differences. The lowest beds (FAR 4A) are characterized by the presence of both 
Patrognathus variabilis gen. et sp. nov. and Polygnathus inornatus inornatus, together 
with Clydagnathus gilwernensis gen. et sp. nov., and Polygnathus communis. The 
first and third of these species occur together in the lowest zone of the Avonian (the 
Patrognathus variabilis-Spathognathodus plumulus plumulus Zone) but Polygnathus 
inornatus inornatus is confined to the overlying zone, where it occurs with P. 
inornatus rostratus subsp. nov., which is found in the immediately overlying sample 
at Farlow (FAR 4), and P. lobatus s.l. which is found in the next overlying sample 
at Farlow (FAR 5). In the Avon Gorge, P. variabilis is associated with Poly- 
gnathus inornatus in this zone. The lowest K Beds of Farlow thus appear younger 
than those of the North Crop or the Avon Gorge. Furthermore, Sample FAR 5 
also contains Spathognathodus cf. robustus, S. crassidentatus , 5. elongatus and S. 
tridentatus, all of which are characteristic of the Spathognathodus cf. robustus- 
Spathognathodus tridentatus Zone of the North Crop and Avon Gorge. It therefore 
appears that the K Zone at Farlow represents a very condensed succession, the 
overlying beds of the K Zone at Farlow yielding an almost identical fauna to that 
of Sample FAR 5. 

The Z Zone strata at Farlow are marked by the appearance of Spathognathodus cf . 
cristulus and Ligonodina beata nom. nov. in the lowest beds (ORZ 1) and Spathog- 
nathodus costatus costatus, and Clydagnathus darensis gen. et. sp. nov. in the overlying 
beds (ORZ 2). These species are characteristic of the Spathognathodus costatus 
costatus-Gnathodus delicatus Zone, as is Clydagnathus unicornis gen. et sp. nov., 
which occurs in the overlying beds (ORZ 3). A single specimen of Gnathodus 
antetexanus in Sample ORZ A3, represents an anomalous faunal association, since 
its first appearance in the Avon Gorge is in beds of Z2 age. 

(iii) Yorkshire (Fig. 54). 

A reconnaissance sampling programme of the Yoredale succession has yielded 
abundant and well preserved conodont faunas characteristic of the higher Avonian 
zones of the South Western Province. Although we have dissolved 7 kilogrammes 
of the Hawes and Gayle Limestones, the beds have yielded no diagnostic conodonts. 
The Hardraw Scar and Simonstone Limestones contain Gnathodus mononodosus sp. 
nov. and G. homopunctatus and thus fall within the G. mononodosus Assemblage Zone. 
The fauna of the overlying Middle Limestone is marked by the first appearance of 
Gnathodus girtyi collinsoni subsp. nov., and the Five Yard Limestone is characterized 
by the first appearance of G. girtyi turritus. These limestones therefore represent 
the G. girtyi collinsoni Zone. Although Varker (1967) has suggested that species of 
the genus Apatognathus may provide a useful basis for zonation and correlation in 
the Yoredales, we have found the genus to be rare, rather than common, as he 
claims, and we do not consider it useful in correlation. 






BRITISH AVONIAN CONODONT FAUNAS 



49 



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50 BRITISH AVONIAN CONODONT FAUNAS 

(iv) Scotland (Figs. 55-58). 

Our general descriptions of Scottish faunas represent only a reconnaissance study, 
our object being to discover whether or not our Avonian zones could be recognized 
there, rather than to provide any comprehensive solution to the complex problems of 
correlation of the Carboniferous of that area. 

We have suggested a provisional application of our zonal scheme to Scotland (Fig. 
15), but have made no precise correlations of individual limestones within particular 
zones, although we believe this will later prove possible. 

Dunbar 

In Dunbar the Long Craig Upper Limestone, which was sampled at 6" intervals 
(DUN 52-71) has a typical G. mononodosus Assemblage Zone fauna, which contains a 
relatively large proportion of mestognathids. The general aspect of this fauna is 
strongly reminiscent of the uppermost D2 Subzone of the North Crop. The over- 
lying Skateraw Lower Limestone (DUN 72, 73) yields a typical G. girtyi collinsoni 
Zone fauna although G. g. collinsoni subsp. nov. itself is present only in the higher of 
two limestone samples. This may suggest that the limestone is transitional between 
this and the underlying zone. The Skateraw Middle Limestone (DUN 74, 82) is 
barren in its lowest sample, but the overlying sample (DUN 75) yields the first 
specimens of G. girtyi turritus, a subspecies which first appears in the upper beds of 
the D3 Subzone on the North Crop. This subspecies continues to be a characteristic 
member of faunas of higher beds. The Barness East Limestone (DUN 87, 88), 
although it has yielded only small faunas, is characterized by a very high proportion 
of cavusgnathids, including both C. naviculus and C. convexus (Fig. 57). 

Midlothian 

Although the limestones of the Lower Limestone Group of Midlothian (NGL 1-17, 
VEX 1, BIL 100-3) have provided no diagnostic species which enable us to correlate 
them with a precise Avonian conodont zone, the overall aspect of their faunas is 
strikingly similar to those of the D3 Subzone of the North Crop. The presence of 
subspecies of G. girtyi and especially the first appearance of G. g. turritus in the 
Vexhim Limestone are useful indications of the general age of these strata (Fig. 56). 

The Gilmerton Limestone (GILM 1-7) was collected from the best available section 
in Midlothian, but this was not the type locality, although we have included it in 
Fig. 56 in the position of the type Gilmerton Limestone in the Lower Limestone 
Group succession. It has a fauna of blades, which are more characteristic of higher 
levels within the D3 sequence. We therefore suspect that the identification of the 
limestone at a quarry one mile S.S.E. of Carlops as the Gilmerton Limestone, as given 
in the Midlothian Coalfield Memoir (1958 : 20), is incorrect. 

Fife 

The Calciferous Sandstone Measures of Eastern Fife are characterized by relatively 
few limestone bands in a thick succession of dominantly clastic strata and coals. 



BRITISH AVONIAN CONODONT FAUNAS 51 

Only three samples (ANS 15, 43, 388) have yielded any conodonts, and of these there 
are few diagnostic species, although the presence of subspecies of G. girtyi indicates an 
overall correlation with the D Zone of the North Crop (Fig. 55). 

The Lower Limestone Group has yielded a small fauna from the Hurlet Limestone 
(HURLET A, C, E) which is characterized by G. girtyi girtyi and G. girtyi simplex. 
The Lower Hosie Limestone (HOSIE 1) yields a larger but essentially similar fauna, 
but the Middle Hosie Limestone (HOSIE 2A-C) has yielded over 1,000 conodonts 
and is characterized by G. girtyi collinsoni subsp. nov., as well as G. mononodosus 
sp. nov. and G. nodosus, which suggests a correlation with a high level in the D3 
Subzone of the North Crop. 

Ayrshire 

The Broadstone Limestone (BRAU 1-8) yielded a very meagre conodont fauna, 
having an average yield of only one conodont per kilogram of rock. The fauna is 
characteristic of the Cavusgnathus unicornis-Apatognathus Zone (Fig. 58). 

The Dockra Limestone (BRAU 9 and 10) yields a large and well preserved conodont 
fauna. G. girtyi simplex and G. girtyi girtyi each represent almost one third of the 
total specimens in each sample studied. The presence of G. girtyi turritus at the base 
of the Dockra Limestone shows this to be within the G.g. collinsoni Zone. 

The Hosie Limestones from Glengarnock (GLEN 1-19) have yielded abundant 
and well preserved conodont faunas, which include three specimens of G. g. turritus, 
which is indicative of the G.g. collinsoni Zone. 

The Index Limestone (DR IN i-GO IN 3) of Ayrshire has yielded faunas which are 
dominated by Gnathodus girtyi girtyi, G. girtyi simplex and G. girtyi collinsoni 
subsp. nov., as well as other species characteristic of the Gnathodus girtyi collinsoni 
Zone of the North Crop. 

The Lower Linn Spout Limestone (LINL, 1, 3) has yielded only five conodont 
specimens. These include G. girtyi girtyi, Mestognathus sp. and Magnilaterella sp. 
which in themselves are not diagnostic. 

The Upper Linn Spout (U.LIN 1-7) has a small fauna which includes G. bilineatus, 
G. mononodosus sp. nov., G. nodosus and G. commutatus. 

We can make no precise correlation of this formation, but, clearly, the presence of 
some 300 ft. of underlying strata within the G. girtyi collinsoni Zone of Ayrshire 
implies a relatively young age. We have assigned the Upper Limestone Group to the 
Eumorphoceras Zone on the basis of Currie's (1954 : 535) goniatite faunas from the 
Index Limestone. 

Roxburghshire 
The main Algal " Series " of Garwood in Harden Burn yielded abundant and well 
preserved conodont faunas. These were dominated by the Polygnathus lacinatus 
group and other species including Cavusgnathus cristatus and Taphrognathus varians. 
In spite of some differences between this fauna and those of the Avon Gorge, the 
presence of polygnathids shows the Roxburghshire faunas to be equivalent to the 
early C Beds of the Avon Gorge. This accords well with the tentative Ci age 
assigned to these beds by Garwood (1931). 



52 BRITISH AVONIAN CONODONT FAUNAS 

Summary 

Our overall Scottish correlations show a very close similarity to those proposed by 
Currie (1954, Table 1) on the basis of her goniatite studies. The only difference 
involves the first appearance of G. girtyi collinsoni subsp. nov. in the Middle Hosie 
Limestone of Fife. 

On the basis of this we have proposed the tentative correlation shown in Fig. 15, 
but it seems probable that the absence of this subspecies from underlying strata is 
the result of the relatively poor yields of the Lower Hosie (29 individual conodonts) 
and Hurlet Limestones (15 conodonts). 

This diagnostic subspecies is represented by less than 3 % of the total fauna of each 
of the two overlying Middle Hosie samples, each of which comprises more than 400 
identifiable conodonts. 

(e) Correlation of the Avonian with Europe and North America 

The purpose of this section is to discuss the value of conodonts in the correlation 
of the British type Avonian section with type sections in North America and Western 
Europe. The sections in the Mississippi Valley, the conodont faunas of which were 
described by Collinson, Scott & Rexroad (1962), are taken as standard sections for 
North America, and the West German Lower Carboniferous sections, the conodont 
faunas of which were described by Bischoff (1957) and Voges (1959), are taken as 
standard sections for Western Europe. We have also made provisional correlations 
with the Franco-Belgian Tournaisian Vis£an succession, basing our comparisons on 
the faunas reported, but not described, by Conil, Lys and Mauvier (1964). 

The general results of this correlation are most gratifying. We have been able to 
suggest the relative equivalence of most of the various divisions of the North 
American, German, French, Belgian and British successions with a sufficient degree 
of confidence and precision to provide a satisfactory overall stratigraphic control. 
In those cases where our correlation is more tentative, we have discussed the limits of 
uncertainty, and these are seldom great. We have had the great advantage of 
working in virtually continuous Avonian rock sections, and some of the present 
anomalies between our faunal successions and those of other areas, such as Germany, 
and, to a lesser extent, the Mississippi Valley, probably lie in the scattered outcrops 
on which the latter are based. More information is needed from all areas before the 
present faunal similarities and differences can be fully interpreted. 

(i) North America and West Germany 

The K and Z Zones oj the Avonian. 

The K and Z Zones of the Avonian are, in many respects, the most difficult part 
of the succession to correlate with other areas, largely because of the absence from 
them of some zonal species, and the presence of new genera and species which are, 
at present, not known with certainty from other areas. 

An important element of the K Zone fauna is the group of new species, which are 
confined to that zone ; these include Patrognathus variabilis gen. et sp. nov., Clyda- 



BRITISH AVONIAN CONODONT FAUNAS 53 

gnathus gen. nov. and Spathognathodus plumulus plumulus sp. nov. Although these 
species are new, they show some resemblances to specimens described from other 
areas. 

Klapper & Glenister (1966) have described faunas from the Canning Basin of 
Western Australia. Their " ? Scaphignathus velifera " is, according to Dr. Klapper 
(personal communication), probably congeneric with Clydagnathus, having a large 
basal cavity, which removes it from Scaphignathus. This species occurs in two 
samples. In one of these, it is not associated with other conodonts, and lies strati- 
graphically about 150 ft. below Spathognathodus aculeatus. In the other, it occurs 
with that species and with Palmatolepis glabra subsp. indet. It is clearly, therefore, 
of Upper Devonian age in this area. This does not necessarily imply an Upper 
Devonian age for the K Zone of the Avonian, however. The resemblance of the 
Australian specimens to those from the K Zone is not exact, and they may represent 
distinct species. The association of the Australian specimens with 5. aculeatus 
implies an age within the costatus Zone and the Tni a of Belgium, but the absence of 
S. aculeatus in the Avonian K Zone conodont faunas suggests that they are of younger 
age. 

The presence of Spathognathodus costatus in the K Zone of the Avonian could imply 
an Upper Devonian age, but 5. costatus, as we have now defined it, differs from S. 
costatus of German authors. The relative position of other Avonian genera makes a 
Carboniferous age even more probable. Our S. costatus is confined to beds in the 
Avonian lying above both Siphonodella and our single specimen of Elictognathus. 
Furthermore, the gnathodids, although they first occur 150 ft. above the position of 
5. costatus in the Avon Gorge, are advanced species which are of undoubted Carboni- 
ferous age in other areas. The earlier species of Gnathodus (G. kockeli etc.) are not 
represented in the Avonian faunas. 

Bouckaert & Ziegler (1965) have described a Fammenian conodont fauna from 
Belgium, in which are found five specimens of Scaphignathus veliferus (1965, PI. 5, 
figs. 5-7) in a sample from the Montfort section at Esneux. These specimens 
probably represent the genus Clydagnathus, although they do not appear conspecific 
with forms from the K Zone. 

The genus Palmatolepis is characteristic of the Upper Devonian but Bischoff (1957) 
and Voges (1959) have reported Palmatolepis in the basal Cu I beds of West Germany. 
In North America, in the Mississippi Valley, Palmatolepis is abundant in the Saverton 
Shale, common to rare in the Louisiana Limestone and occurs rarely in the basal 
beds of the Hannibal. Collinson (1961) stated that " the occurrence of Palmatolepis 
glabra and Palmatolepis gracilis in the European Lower Carboniferous, as well as in 
the Mississippi Valley Hannibal Formation, may represent stratigraphic admixture, 
but it seems more likely that they are indigenous ". Specimens of the vast majority 
of Upper Devonian faunas yield abundant Palmatolepis, and the absence of palmato- 
lepids in the Avon Gorge provides some negative evidence in support of the assign- 
ment of the lowermost strata to the Carboniferous. 

Fewer than 2 % (Klapper & Furnish, 1962 : Ziegler 1962, table 7 : Bouckaert & 
Ziegler 1965, Chart 9) of the Upper Devonian faunas described lack Palmatolepis, and 



54 BRITISH AVONIAN CONODONT FAUNAS 

the genus is present in Devonian faunas in southwestern England. We stress that 
these are negative data, however ; indeed, it seems possible that a few Lower 
Carboniferous faunules may contain indigenous palmatolepids. 

It is possible that our Lower K faunas are close to the fauna briefly described by 
Bouckaert & Ziegler (1965, Chart 9, p. 25) from the section at Huy 2 in Belgium. 
The highest part of this section (19) contains a new genus (not described, illustrated, 
or mentioned in the text) together with S. aculeatus E. R. Branson and Pseudopoly- 
gnathus dentilineatus E. R. Branson. The first of these two species may represent 
S. plumulus. Bouckaert & Ziegler also record from the same sample (1965 : 17), a 
single specimen of a form " which seems to represent a new trend evolved from 
Spathognathodus costatus " (PI. 4, fig. 12 and p. 27 : Pseudopolygnathus sp.). This is 
close to our Pseudopolygnathus vogesi sp. nov. A Lower Tournaisian age for this 
part of the Belgian section has been suggested by Conil (1964) on the basis of the 
foraminifera, and Streel (1966) states that the spores indicate a Devonian age. 

Klapper & Sandberg (1967 : B 52) have found the genus Patrognathus in a very 
thin interval of strata in Wyoming (the Windy Gap Formation). It is associated 
with Siphonodella sulcata, a species that was also recovered by these authors from 
the upper part of the G. kockeli-P. dentilineatus conodont zone in Germany (Voges 
1959, text-fig. 1, Samples 3 and 4). 

An undescribed conodont fauna from the Lower Pilton Beds contains Spatho- 
gnathodus plumulus sp. nov., Pseudopolygnathus vogesi sp. nov. and representatives of 
the genus Clydagnathus (J. W. Williams, personal communication) . The Lower Pilton 
Beds are considered to be of Wocklumeria age (Goldring 1955). However, no speci- 
mens of the genus Patrognathus have as yet been found in the Lower Pilton Beds. 
Thus the Lower Limestone Shale appears to be younger than the Lower Pilton Beds. 
The conodont fauna of the Lower Pilton Beds is unlike the fauna from the Wock- 
lumeria to VI Zone described by Ziegler (1962). It is closer to the fauna described 
by Bouckaert & Ziegler (1965), from the uppermost Fammenian at Huy. 

All the evidence points to the conclusion that a gap in the conodont sequence is 
present in the type section of the Devonian-Carboniferous boundary in the Honnetal 
railway cutting. The Huy section of Fammenian age is younger than the type to VI 
strata at Honnetal, but on goniatite and spore evidence it is still Devonian. The 
base of the Lower Limestone Shale is younger than the Huy section (on the basis of 
the absence of the genus Patrognathus in the Huy section), but is older than the base 
of the Tournaisian in the Honnetal railway cutting. 

Thirty feet above the base of the K section in the North Crop a single specimen of 
Elictognathus has been found. Elictognathus makes its first appearance in North 
America at the base of the Siphonodella sulcata Assemblage Zone which is near the 
the base of the Hannibal Formation, and is correlated with the middle part of the 
Lower Carboniferous Cu I Zone of Western Europe (Collinson, Scott & Rexroad 
1962). 

Associated with Elictognathus in the Pseudopolygnathus vogesi-Clydagnathus 
Assemblage Subzone of the Avonian is Pseudopolygnathus vogesi sp. nov. This 
species is characteristic of the lower part of the Lower Carboniferous Cu I Zone of 



BRITISH AVONIAN CONODONT FAUNAS 55 

Western Europe (Voges 1959). Collinson, Scott & Rexroad (1962) noted that the 
first appearance of the genus Pseudopolygnathus in the Mississippi Valley was at 
the base of their Gnathodus n. sp. B.-Gnathodus kockeli Assemblage Zone, which is 
confined to the Glen Park and the basal Hannibal Formations and is correlated 
with the lowermost part of the Lower Carboniferous Cu I Zone of Western Europe. 
The upper part of the Pseudopolygnathus vogesi-Clydagnathus Assemblage 
Subzone has specimens of P. inornatus which Ziegler (1962), who referred to 
them as Polygnathus nodomarginatus, found in the Middle and Upper Spathognathus 
costatus Zones, as well as in the G. kockeli-P. dentilineatus Zone. Dr. C. W. 
Collinson (personal communication) has found similar specimens in the Mississippi 
Valley, where they appear to be forerunners of Siphonodella sulcata. These are 
found in abundance, and are associated with Gnathodus kockeli in the base of the 
Hannibal Formation at several localities (just below the lowermost Siphonodella 
Zone). 

The conodont fauna of the K and basal Z Zones of the Avonian is also difficult to 
correlate precisely with the American and West German successions, because of the 
rarity of the genus Siphonodella in the K Zone and its absence in the Z Zone. This 
genus is one of the most useful of all guide fossils in other areas, where individual 
species are distinctive, short ranging, and have a wide geographical distribution 
(Collinson, Scott & Rexroad 1962, Chart 2). In North America and West Germany 
ranges of individual species have been used to define the boundaries of conodont 
assemblage zones. 

In the Avonian, the genus Siphonodella is confined to the Siphonodella-Polygnathus 
inornatus Assemblage Zone. Specimens from the Avon Gorge, although fractured, 
have rostral ridges and are more advanced in development than Siphonodella sulcata, 
the earliest known species in North America, where it occurs near, but not at, the 
base of the Hannibal Formation. Specimens from the North Crop are identified as 
Siphonodella isosticha. This species in North America ranges from the base of the 
Upper Hannibal Formation to the top of the Upper Chouteau Formation. Thus the 
base of our Siphonodella-Polygnathus inornatus Assemblage Zone cannot be older 
than the base of the upper part of the Hannibal Formation, which is included in the 
lower part of the Siphonodella quadruplicata-Siphonodella crenulata Assemblage Zone 
of the Mississippi Valley. 

Correlation of the base of this zone with our Siphonodella-Polygnathus inornatus 
Assemblage Zone, would make it broadly equivalent to the lower part of the Cu II a 
Zone of the European Lower Carboniferous. This is supported, to some extent, by a 
consideration of the ranges of gnathodid species, which provide a possible correlation 
for the higher part of the Avonian section. 

Klapper (1966) has described a fauna from the Lodgepole Limestone of Montana 
and Wyoming, which is referable to the Lower Siphonodella crenulata Zone (Cu II a) 
of Germany and from the Mississippian part of the Dark Shale Unit, which is referable 
to the Siphonodella-P . triangulus triangulus Zone (Cu I). These faunas are in part 
similar to the Upper K Zone fauna of the Avonian. 

The conodont fauna of the Spathognathodus robustus-Spathognathodus tridentatus 



5 6 BRITISH AVONIAN CONODONT FAUNAS 

Assemblage Zone is similar to that described by Branson & Mehl (1934A) from the 
Bushberg Sandstone of Missouri, while the fauna of the basal Spathognathodus 
costatus sulci ferus-Gnathodus delicatus Assemblage Zone is similar to that of the 
Hannibal Formation of Missouri described by E. R. Branson (1934). 

Our faunas from the K and Z Zones seem to agree closely with those described by 
Branson & Mehl (1934A) from the Bushberg, E.R.Branson (1934) from the Hannibal, 
and Cooper (1939) from the pre-Welden Shale Formations. This suggests that the 
biostratigraphic zones set up by Collinson, Scott & Rexroad (1962) may not be fully 
representative of the conodont faunas of the lowermost Lower Carboniferous of the 
whole of North America, as opposed to the Illinois Basin. Further work on Missouri 
and Oklahoma sections would probably prove useful in correlation between North 
America and the South West Province of Great Britain. 

Gnathodus delicatus makes its first appearance in the Avonian 34 ft. (Sample ZLA 6 
North Crop) from the top of the Spathognathodus costatus costatus-Gnathodus delicatus 
Assemblage Zone. In North America this species first appears at the base of the 
Chouteau Formation, in the top of the Siphonodella quadruplicata-Siphonodella 
crenulata Assemblage Zone, but little is known about the distribution of Upper 
Hannibal gnathodids, and it is therefore possible that Gnathodus delicatus may 
appear lower in the section. The top of the Hannibal Formation is the zone of few 
gnathodids of Collinson, Scott & Rexroad (1962). A similar zone of few gnathodids 
is also present in Germany. Branson & Mehl (1938A : 136) remarked that the 
Chouteau conodont assemblage is characterized by the introduction of Gnathodus. 
The base of the Chouteau Formation also corresponds to the oldest stratigraphical 
occurrence of the upper zone of Gnathodus shown by Collinson, Scott & Rexroad 
(1962, Chart 3). 

The earliest occurrence of Gnathodus delicatus in the Avon Gorge, which is some- 
what higher (base Sample Z 29) in the section than the earliest occurrence on the 
North Crop, is represented by relatively large numbers of specimens, in contrast to the 
few specimens found in its first occurrence on the North Crop. The earliest occur- 
rence of Gnathodus delicatus on the North Crop may be correlated to the Siphonodella 
quadruplicata-Siphonodella crenulata Assemblage Zone occurrence of North America, 
which lies within the Zone of few gnathodids, whereas the Avon Gorge first occurrence 
may be correlated with the abundant occurrence of Gnathodus delicatus in North 
America, near the upper limit of the Siphonodella isosticha-Siphono delta cooperi 
Assemblage Zone, which occupies the upper part of the Chouteau Formation and is 
correlated with the upper part of the European Lower Carboniferous Cu II a Zone. 

Rexroad & Scott (1964) described the conodont faunas from the Siphonodella 
isosticha-Siphonodella cooperi, Gnathodus semiglaber-Pseudopolygnathus multistriatus, 
Bactrognathus-Polygnathus communis and Bactrognathus-T aphrognathus Assemblage 
Zones, when they described the conodont fauna of the Rockford Limestone and New 
Providence Shale. They noted (Table 2 : 15) that Gnathodus delicatus was most 
abundant in the Siphonodella isosticha-Siphonodella cooperi Assemblage Zone, 
Gnathodus semiglaber most abundant in the overlying Gnathodus semiglaber-Pseudo- 
polygnathus multistriatus Assemblage Zone and Gnathodus antetexanus most 



BRITISH AVONIAN CONODONT FAUNAS 57 

abundant in the overlying Bactrognathus-Polygnathus communis Assemblage Zone. 

In the Avonian of the Avon Gorge a similar change in the gnathodid fauna is seen. 
Gnathodus delicatus occurs near the base of the Z2 Subzone, Gnathodus semiglaber is 
present in the upper part of Z2 and Gnathodus antetexanus first appears in the upper 
part of Z2 and ranges into the lower part of Ci (Fig. n). 

The occurrence of gnathodids in Germany provides conflicting data for comparison. 
Ziegler (i960, 1963) has described gnathodids identical to those of the middle Poly- 
gnathus lacinatus Zone of the Avonian (Samples Z 28-Z 30). One of his faunules of 
anchoralis age (i960) also contained Siphonodella and Mestognathus, but the other 
yielded no representatives of Siphonodella. The anchoralis fauna of Germany, as at 
present understood, contains the simultaneous first appearance of several species of 
Gnathodus, which appear at different horizons in the Lower Carboniferous of Britain 
and North America. We interpret this as partly the result of Bischoff & Voges' 
limited stratigraphic sections and partly the result of the more recent taxonomic 
refinements, which would now require the revision of the earlier specific nomenclature 
of these authors. 

Specimens referable to G. semiglaber, G. typicus, G. antetexanus and G. girtyi all 
first appear at the base of the anchoralis Zone. It appears that the anchoralis Zone 
as presently defined in Germany occupies a greater period of time than hitherto 
thought and that the Cu II (3-y with which it is generally equated could include the 
time interval Upper Z2-Upper C2 in the Avonian and at least from the top of the 
Chouteau Formation to the top of the Burlington Formation in North America. 

If the first appearance of species is used as the basis of correlation, the oldest 
occurrence of Gnathodus delicatus in the Avonian is in the Spathognathodus costatus 
costatus-Gnathodus delicatus Zone. In North America it first occurs in the Siphono- 
della isosticha-S. cooperi Zone, which might thus be interpreted as being equivalent 
to the Avonian Zone. This would make it equivalent to the Upper Chouteau, and 
to the upper part of Cu II a of the German succession (Figs. 12, 16). Collinson, 
Rexroad & Scott (1962) noted that the top of the Siphonodella isosticha-Siphonodella 
cooperi Assemblage Zone was marked by a major unconformity in the Mississippi 
Valley and was a cut-off horizon for Gnathodus delicatus. This is one possible 
correlation, but the rarity of siphonodellids in the Avonian makes any such correla- 
tion based on " first appearances " of species tenuous, and other aspects of the fauna 
suggest a somewhat younger (Chouteau) age for the Avonian Zone. 

The Siphonodella-Polygnathus inornatus Zone is also characterized by the presence 
of Polygnathus inornatus s.l. and Siphonodella isosticha, both of which are character- 
istic species of the Siphonodella isosticha-S. cooperi Zone of the Mississippi Valley 
(Collinson, Scott & Rexroad 1962 : 21). Correlation of these two zones would thus 
appear an alternative valid solution to the problem, the general absence of earlier 
transitional siphonodellids in the Avonian being interpreted as a result of geographic 
faunal variation, either in the absence of whatever conodont-bearing group they 
represented, or, more probably, their " local " functional replacement by broadly 
homologous polygnathids (Fig. 16). 

Such a possible correlation is supported by the fact that in the Bonaparte Gulf of 



58 



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BRITISH AVONIAN CONODONT FAUNAS 59 

Australia one of us (in Jones & Druce 1966) has recently discovered a series of 
abundant conodont faunas extending through some 3,000 ft. of Lower Carboniferous 
strata. There is a striking resemblance between the Australian and the Avonian 
conodont successions, and although Siphonodella is abundant in the Australian 
faunas, it does not extend up as high as the Spathognathodus costatus group (Fig. 
16). This could mean that all the Siphonodella zones of the Mississippi Valley lie 
below the first occurrence of 5. costatus in the Avonian, and would therefore be of K 
age. 

The other implication of such a correlation would be that the North American and 
the German successions are more incomplete than has formerly been supposed, for it 
would be difficult to find any North American equivalent of the two overlying 
Avonian assemblage zones, if the correlation of the Avonian Polygnathus lacinatus 
Zone and the Mississippian Gnathodus semiglaber-Pseudopolygnathus multistriatus 
Zone (which seems to us to be very well established, p. 57) is accepted. This would 
suggest that the unconformity known to exist beneath the Sedalia Formation of the 
Mississippi Valley, is of greater magnitude than is generally assumed. 

There may not be such a break in the Oklahoma or parts of the Missouri successions 
(Cooper 1939 ; Branson & Mehl 1934A : 265). The Rockford Limestone fauna 
(Rexroad & Scott 1964) reveals an apparent transition in northern Indiana from the 
Siphonodella isosticha-S. cooperi Zone into the Gnathodus semiglaber-Pseudopoly- 
gnathus multistriatus Zone, however, and represents an anomaly if the present 
correlation is accepted, although most of the sections come from cores. There is, 
however, an unconformity in southern Indiana between the Rockford and the over- 
lying New Providence Shale. Even in areas of apparent transition of the two 
assemblage zones within the Rockford Limestone, the faunal transition is abrupt 
(Rexroad & Scott 1964, Table 1). Rexroad & Scott (1964 : 16-17) have written 
" Although a number of species are common . . . this break between the Kinderhook 
and Osage Series is unusually well marked. The faunal break is sharp, but a number 
of species confined to the lower zone gradually decrease in number upward. Thus an 
unconformity within the Rockford at the Kinderhook-Osage boundary is not 
necessarily indicated. At the type section near Rockford (locality 10) the formation 
is exposed only in the bed of the East Fork of White River, and even at low water the 
evidence relating to a possible unconformity cannot be interpreted." 

It may also be that the overlap of the Siphonodella and anchoralis faunas in 
Germany implies a stratigraphic break between them, in which case part of the 
Upper Cu II a and Lower Cu II (3 could be unrepresented. One of the major problems 
concerning the anchoralis fauna is its patchy geographic distribution (p. 65). It is 
possible that its limited distribution in North America (it is recorded from the 
Pierson Formation of Missouri and the " Sedalia " of Illinois, above the uncon- 
formity) may mean that in places it is represented by the unconformity which we 
have postulated. 

This alternative correlation has stressed the inadequate numbers of siphonodellids 
in British Lower Carboniferous faunas, and its weakest point is the lack of a more 
detailed series of species of this genus in the Avonian. The first provisional correla- 



60 BRITISH AVONIAN CONODONT FAUNAS 

lation, in which the ranges of gnathodid species were compared, is also limited by a 
comparable, tantalizing " zone of few gnathodids " in the Middle and Upper 
Hannibal of North America, and if, as we believe, both correlations are equally 
reasonable, they are also equally vulnerable, because of a comparable lack of 
detailed phylogenetic development in Britain and the United States. 

The present available data are insufficient to allow us to make a final choice 
between the two alternative correlations ; although we have shown the second on 
our main correlation table (Fig. 12), we have summarized the evidence for both 
on Fig. 16). The total stratigraphic differences involved between them are not 
great, and it is perhaps a paradoxically satisfying aspect of the precision which we 
believe conodonts offer, that we should be dissatisfied with an uncertainty of some 
80 ft. in such a transatlantic correlation. 

A new conodont fauna associated with the goniatites Protocanites and Muen- 
steroceras from the Berwick Formation of Australia (Dr H. T. B. Jenkins, personal 
communication) contains a fauna which is similar to the Z Zone fauna of the Avonian 
in many respects. The pseudopolygnathids are identical to Zi and Lower Z2 speci- 
mens. Associated with the pseudopolygnathids are many gnathodids, most of which 
are new species, although a few are similar to G. punctatus, a species characteristic of 
the upper part of Z2. Two specimens of Bactrognathus also occur in the Australian 
fauna, suggesting that Bactrognathus is older than has hitherto been thought likely. 

The fauna of Samples Z 31 to Z 38 with Gnathodus semiglaber and Pseudopoly- 
gnathus multistriatus is similar to that of the Gnathodus semiglaber-Pseudopoly- 
gnathus multistriatus Assemblage Zone of the Mississippi Valley. This Assemblage 
Zone coincides with the " Sedalia " Formation of the Mississippi Valley and has been 
correlated with the lowermost part of the Cu II (3 Zone of Western Europe. Dr W. 
Ziegler (personal communication) believes that the gnathodid fauna of Samples 
Z 34-Z 38 is identical to that found in Western Europe in beds equivalent to the 
Siphonodella crenulata Zone (Voges 1959) and thus of Cu II a age. 



C Zone. 

In the upper part of the Z Zone and in the lower part of the Laminosa Dolomite, 
Gnathodus antetexanus has been found, associated with Pseudopolygnathus cf. 
triangulus triangulus, Polygnathus communis and Polygnathus lacinatus. The lower 
limit of the Bactrognathus-Polygnathus communis Assemblage Zone in the Mississippi 
Valley coincides with the earliest abundance of Gnathodus antetexanus, and the upper 
with the youngest stratigraphical occurrence of Polygnathus communis. In the 
Avonian of the Avon Gorge, the youngest stratigraphical occurrence of Polygnathus 
communis is in the middle of the Laminosa Dolomite (the base of Sample C 10). 
The Bactrognathus-Polygnathus communis Assemblage Zone is characterized by the 
presence of Polygnathus communis, Pseudopolygnathus multistriatus, Pseudopoly- 
gnathus triangulus pinnatus and by being the zone of abundant Gnathodus ante- 
texanus. Samples Z 38-C 9 are correlated with this Assemblage Zone. In North 
America, the zone extends from the base of the Fern Glen Formation to the top of 



BRITISH AVONIAN CONODONT FAUNAS 61 

the Middle Burlington Formation. In Western Europe it ranges from upper Cu II (3 
into lower Cu II y. 

In West Germany Bischoff (1957) recorded the first appearance of Mestognathus 
beckmanni at the base of Cu III a, but Voges (1959) found a single specimen near the 
base of Cu II (3/y. Kronberg, Pilger, Scherp and Ziegler (i960) also found Mesto- 
gnathus beckmanni in beds of Cu II (3/y age. Meischner (1962) in his chart of strati- 
graphic ranges (p. 31, fig. 10) showed the stratigraphic range of Mestognathus 
beckmanni as commencing at the base of Cu II (3/y. The lowest occurrence of M. 
beckmanni in the Avonian is in the upper part of the Laminosa Dolomite (the base of 
Sample C 15). Thus the upper part of the Laminosa Dolomite appears to be of 
Cu II p/y age. 

In North America the base of the Bactrognathus-Taphrognathus Assemblage Zone 
is marked by the highest occurrence of Polygnathus communis, and the top by the 
lowest abundant occurrence of Gnathodus texanus, which makes its first appearance 
near the top of the zone. The youngest stratigraphic occurrence of Polygnathus 
communis in the Avonian is in the middle of the Laminosa Dolomite. It is con- 
sidered that the middle of the Laminosa Dolomite, above the youngest occurrence of 
Polygnathus communis (base Sample C 10), corresponds to the base of the Bactro- 
gnathus-Taphrognathus Assemblage Zone of North America. In North America this 
zone is confined to the upper part of the Burlington Formation and is correlated by 
Collinson, Scott & Rexroad (1962) with the upper part of the European Cu II (3/y 
Zone. Since Mestognathus has not been recorded from North America, our inter- 
mediate faunas provide important confirmation of this correlation. 

The Caninia Oolite in the Avon Gorge is characterized by the presence of two 
species, Polygnathus bischoffi sp. nov. and Mestognathus beckmanni. In Western 
Europe the youngest stratigraphic occurrence of Polygnathus bischoffi sp. nov. is at 
the top of Cu II p/y. Gnathodus texanus s.s. occurs with Mestognathus beckmanni and 
Polygnathus bischoffi sp. nov. in the Caninia Oolite of Fall Bay, Gower. Since the 
youngest occurrence of Gnathodus texanus s.s. in North America is near the top of the 
Bactrognathus-Taphrognathus Assemblage Zone, the upper part of the Laminosa 
Dolomite and the Caninia Oolite are correlated with the Taphrognathus-Bactro- 
gnathus Assemblage Zone and with the upper part of the European Cu II (3/y Zones. 

A conodont fauna from Askeaton, Eire, contains specimens of G. texanus, P. 
triangulus pinnatus and G. girtyi. The specimens of G. girtyi are identical to those 
illustrated by Hass (1953) and clearly have developed from G. texanus. The 
Askeaton fauna is therefore younger than the Caninia Oolite fauna and is best 
correlated with the Caninia Dolomite. 

S and D Zones. 

The Cavusgnathus unicornis-Apatognathus libratus and the Taphrognathus varians- 
Cavusgnathus-Apatognathus Zones of the Avonian cannot be precisely correlated 
with the American assemblage zones. Although they have elements in common 
with both the Taphrognathus varians-Apatognathus and the Apatognathus? geminus- 
Cavusgnathus Assemblage Zones of the Mississippi Valley, there are also important 



62 BRITISH AVONIAN CONODONT FAUNAS 

differences between the two faunal successions. The Taphrognathus varians- 
Apatognathus Assemblage Zone includes the Warsaw, Salem and the lower part of the 
St. Louis Formations, and it is probably equivalent to the upper part of the Cu II 8 
Zone of Western Europe. The limits of this assemblage zone were defined by 
Collinson, Scott & Rexroad (1962) as follows : " The lower limit is marked by the 
lowermost occurrence of Apatognathus? in the Valmeyeran Series plus the highest 
occurrence of common Taphrognathus varians. The upper limit is distinguished by 
the lowermost occurrence of Cavusgnathus and the youngest occurrence of Taphro- 
gnathus as well as by the lower limit of the upper zone of abundant Apatognathus ". 

The lowest stratigraphic occurrence in the Avonian of specimens identical to the 
apatognathids illustrated by Rexroad & Collinson (1963) is near the base of Ci. 
Taphrognathus does not appear in the Avonian until the upper part of the S Zone, 
well above the first appearance of Cavusgnathus. Specimens transitional between 
Cavusgnathus and Taphrognathus, identical to those illustrated by Rexroad and 
Collinson from the boundary between the lower and upper St. Louis Formation, are 
found in Samples S 49 to S 58 of the Avonian. Cavusgnathus first appears in the 
Avonian in the middle of the Caninia Dolomite, well above the first appearance of 
Apatognathus, and well below the first appearance of Taphrognathus. In North 
America, however, the first appearance of Cavusgnathus is above the first appearance 
of Taphrognathus and Apatognathus. 

In the Scottish conodont faunas, Taphrognathus varians occurs with Polygnathus 
lacinatus, a species which in the Avonian is common in the upper part of Z2 and in the 
C Zone. Thus it would appear that the lowest occurrence of Taphrognathus in 
Britain may be considerably lower than that noted from the Avonian of the South 
West Province and it would then correspond more closely with the North American 
occurrence. 

The Apatognathus geminus-Cavusgnathus Assemblage Zone (Upper S2-Di of the 
Avon Gorge) is equivalent to the upper part of the St. Louis Formation of the 
Mississippi Valley and to the basal Cu III a of Germany. 

In Germany, Mestognathus beckmanni ranges from the base of Cu II (3/y (and may 
extend into Cu II a) to the middle of Cu III y (Bischoff 1957) although Meischner 
(1962) gives the upper limit as Middle Cu III (3. Gnathodus bilineatus is present in 
the Cu III and E Zones of Germany and Britain (Collinson & Druce in press : Higgins 
1961), and G. girtyi girtyi ranges from Cu II y into the Namurian (Bischoff 1957), 
although Meischner (G. girtyi Form A = G. girtyi girtyi) restricts it to the Cu III a 
Zone, with the possibilities of homeomorphic development throughout Cu III. In 
view of Bouckaert & Higgins' (1963) record of the species from the E2a of the Belgian 
Dinant Basin and its presence in Pi and P2 of the Yoredale succession, the German 
ranges cannot be used as the basis of correlation. The absence of the gnathodids, 
G. semiglaber and G. texanus, as well as species of the genus Polygnathus, from this 
Lower D2 Subzone indicates that it is younger than Cu II y. 

Meischner (1962 : 31) has shown that G. girtyi simplex (G. girtyi Form B of 
Meischner) first occurs very near the base of Cu III (3, while G. homopunctatus 
occurs just below the base of Cu III (3. Thus the upper boundary of the Mestog- 



BRITISH AVONIAN CONODONT FAUNAS 63 

nathus beckmanni-Gnathodus bilineatus Zone appears to be at the base of the Cu III (3 
Zone, the zone being confined to Cu III a. 

The fauna resembles that of the St. Louis Limestone, and has a very close similarity 
to that of the overlying St. Genevieve Formation. 

The base of D2 in the Avonian is within the Gnathodus bilineatus-Cavusgnathus 
charactus Assemblage Zone of North America. G. bilineatus first appears in the base 
of this zone in the Mississippi Valley, but the details of this North American zone are 
not yet fully studied (Collinson, Scott & Rexroad 1962 : 25). The species first 
appears in the higher part (Unit C) of the Pella Formation of Iowa (Rexroad & 
Furnish 1964). 

One anomalous aspect of this correlation is the reported first appearance of the 
Gnathodus girtyi group at the top of this zone in the Mississippi Valley (Collinson, 
Scott & Rexroad 1962 : 25). 

The Gnathodus mononodosus Zone includes the last appearance of M. beckmanni, 
which is last found in the Middle Cu III (3 of Germany (Meischner 1962). The fact 
that our zone is established on the basis of a new species makes more precise correla- 
tion difficult. G. nodosus, which first appears at the base of this zone in the North 
Crop, first appears in the Middle Cu III (3 zone of Germany (Meischner 1962). 

The overlying Gnathodus girtyi collinsoni Zone represents the first appearance of 
G. girtyi collinsoni (= G. girtyi Form C of Meischner 1962), which first appears at the 
base of Cu III y, in the Middle Rhenaer Kalk of Germany. The last appearance of G. 
homopunctatus on the North Crop falls within this zone, and this is closely similar to 
its last appearance in Germany (Meischner 1962 : 31, Chart 10). The overall aspect 
of this Avonian Zone is similar to that of the pre-Middle Glen Dean Chesterian 
Formations of the Mississippi Valley. 

(ii) France and Belgium 

There are no adequately illustrated accounts of the Lower Carboniferous faunas of 
France or Belgium, and our comparisons are made on the basis of published faunal 
lists. We have not been able to study the original specimens, and our correlations 
are, therefore, tentative and provisional. 

Conil, Lys & Mauvier (1964) have studied the conodont faunas of the Tournaisian 
and Visean in Belgium and France. They showed that Taphrognathus (synonymous 
with Patrognathus gen. nov. or Clydagnathus gen. nov.) occurs in beds that are of 
Tni a -Tn2b age. Associated with Taphrognathus in Tni b are Polygnathus inor- 
natus, Pseudopolygnathus dentilineatus, Elictognathus costatus and Siphonodella 
obsoleta, a fauna which is closely similar to that of the Upper K Zone. In Tn2b 
Siphonodella duplicata, Siphonodella lobata and Siphonodella quadruplicata appear, 
whilst in Tn2 C Siphonodella sexplicata makes its first appearance. 

Tn2c is characterized by the presence of the genera Pseudopolygnathus, Siphono- 
della and Elictognathus. The base of Tn2 C would appear to correlate with the upper 
part of the Middle Hannibal Formation of North America, based on the first occur- 
rence of the species Siphonodella cooperi and Siphonodella sexplicata. 

At the base of Tn3 a in Belgium and France, the following species have their first 



64 BRITISH AVONIAN CONODONT FAUNAS 

occurrence : Gnathodus commutatus, Gnathodus delicatus, Gnathodus semiglaber and 
Polygnathus communis. Siphonodella obsoleta and Siphonodella duplicata are also 
present. 

In the Avonian Gnathodus delicatus first appears in Z x . It is followed in the Lower 
7,2 Subzone by Gnathodus simplicatus and in the upper part of Z2 by Gnathodus semi- 
glaber. Thus the upper part of Z\ and the Z2 Subzone would appear to be broadly 
equivalent in age to Tn3 a . There are, however, two peculiarities in the Franco- 
Belgian Tn3 a conodont fauna : firstly, the late first occurrence of Polygnathus 
communis, and secondly, the occurrence of Pseudopolygnathus triangulus inaequalis. 

Tn3b is characterized in the Franco-Belgian Province by the presence of Gnathodus 
delicatus, Polygnathus communis, Doliognathus excavatus, Scaliognathus anchoralis, 
Hindeodella segaformis, Gnathodus bilineatus, Gnathodus homopunctatus and Gnathodus 
girtyi. 

In Germany two of these species, Scaliognathus anchoralis and Hindeodella sega- 
formis, and also one of the genera, Doliognathus, are confined to the Scaliognathus 
anchoralis Zone (Cu II (3/y). Gnathodus delicatus first appears at the base of the 
anchoralis Zone. The youngest occurrence of Polygnathus communis is within the 
anchoralis Zone. Gnathodus homopunctatus is present at the top of the zone, as too is 
Gnathodus girtyi. 

Gnathodus bilineatus in Germany does not appear until after the youngest strati- 
graphic occurrence of Scaliognathus anchoralis (the anchor alis-bilineatus interval). 
In the Franco-Belgian Province, on the other hand, the first appearance of the two 
species is contemporaneous. 

In the Franco-Belgian Province the youngest stratigraphic occurrence of the genus 
Siphonodella coincides with the oldest stratigraphic occurrence of the genus Scalio- 
gnathus at the base of Tn3 b . In Germany Siphonodella extends into Cu III a in the 
Hartz Mountains of the Sauerland (Voges 1959). It extends into the same zone in 
Spain (Dr W. Ziegler, personal communication) , but in North Africa (Dr G. Bischoff , 
personal communication) it is limited to Cu II. The Genus Elictognathus became 
extinct a short distance beneath the anchoralis Zone, at the base of the upper 
Siphonodella crenulata Zone (Middle Cu II a), whereas, in the Franco-Belgian 
Province, the latter genus became extinct at the base of Tn3 a . Dr S. C. Matthews 
is at present investigating the distribution of the anchoralis Zone fauna in Europe. 

In North America the base of the Sedalia Formation is an unconformity and the 
genera Elictognathus and Siphonodella have their youngest stratigraphic occurrence 
at the top of the Upper Chouteau Formation. Scaliognathus anchoralis first appears 
at the base of the Sedalia Formation. At the base of the Fern Glen Formation the 
genera Doliognathus, Staurognathus and Bactorgnathus first appear. Gnathodus 
delicatus, Gnathodus cf. girtyi, Gnathodus semiglaber , Gnathodus cuneiformis and 
Gnathodus antetexanus also are present above the base of the Sedalia Formation. 

In Germany there is a gap in the known conodont sequence beneath the anchoralis 
Zone. It appears likely, however, that Tn3b of the Franco-Belgian succession is 
equivalent in age to the German Cu II (3/y anchoralis Zone and the Cu II $ anchoralis- 
bilineatus interval combined. It also correlates with the Fern Glen and Burlington 



BRITISH AVONIAN CONODONT FAUNAS 65 

Formations of North America. Pseudopolygnathus dentilineatus of Conil et al. in 
Tn3b is synonymous with Pseudopolygnathus multistriatus of Mehl & Thomas in the 
U.S.A. 

This would also suggest that the Tournaisian-Visean boundary in the cephalopod 
fades of Germany should not be drawn as at present at the top of Cu II a, but higher 
in the succession at the top of Cu II. 

There are, however, two complications. Firstly, the type fossil of the Cu II a 
horizon, Pericyclus princeps, although never recorded from Germany, is recorded from 
the Tn3 C horizon of Belgium. Secondly, Pseudopolygnathus triangulus inaequalis is 
confined to Tn3 a in the Franco-Belgian Province and to the middle of the Cu I in 
Germany. This might imply that the German Upper Cu I and Cu II a horizons are 
equivalent in terms of the Franco-Belgian Tournaisian to the bedding plane boundary 
of Tn3 a -Tn3b, but we have some reservations about the general applicability of the 
subspecies of Ps. triangulus established by Voges. 

In Britain none of the genera Scaliognathus, Staurognathus, Doliognathus, or 
Bactrognathus have been found in the Avonian, although Matthews (1961) did record 
Scaliognathus anchoralis, Hindeodella segaformis and Doliognathus lotus from the 
Lower Carboniferous in East Cornwall. Thus these fossils, characteristic of the 
anchoralis Zone in Germany were present in the British Lower Carboniferous seas. 
One possible explanation of their non-appearance in the Avonian is that the 
anchoralis Zone of Germany is represented in the Avonian by the Z2 Fish Bed, which 
would thus represent a considerable non-sequence. 

Alternatively Scaliognathus anchoralis and its typical zonal associates may be 
limited in their distribution, either by fades or geography. This is supported by the 
fact that in North America, from which it was first described, S. anchoralis is known 
only from Branson & Mehl's type specimen, and further intensive sampling of the 
type locality by Dr. C. W. Collinson has failed to produce even one additional 
specimen (personal communication). It does not seem to be present in Australia, 
although it is abundant in Germany, France, Belgium, Spain and North Africa. 
Some of the typical associated genera display similar anomalies in distribution. 
Doliognathus is abundant in some sections in Germany, but absent in others, even 
though its zonal associates are present in both. It may be that this group of rather 
bizarre genera are components of one or more natural conodont assemblages of 
limited tolerance. If this alternative explanation is correct, the anchoralis Zone of 
Germany may be represented not by a hiatus but by a succession with a different 
fauna in the Avonian. The exact limits of correlation are difficult to determine, 
but would lie within the Upper Z to Lower C Zones. 

It seems possible, however, that the anchoralis horizon is equivalent to the lower 
part of the Caninia Dolomite of the Avon Gorge, which has yielded no conodont 
faunas. 

VI. SYSTEMATIC PALAEONTOLOGY 

The following section contains descriptions of the species recorded in the present 
study. The ranges recorded in the descriptions refer to sample numbers that are 
listed on p. 292. 



66 BRITISH AVONIAN CONODONT FAUNAS 

The following prefixes are used to describe the various collecting areas : 

Avon Gorge : the section at the Avon Gorge, Bristol, and immediately adjacent 

areas (see p. 18 and Figs. 59-69). 
North Crop : the northern limb of the synclinal structure of the South Wales 
Coalfield in Brecknockshire and Monmouthshire (see p. 22 and 
Figs. 7, 70-73). 
Scotland : the various sections from the Midland Valley of Scotland (see p. 29 and 

Figs. 79-91). 
Farlow : the Avonian section at Farlow, Shropshire (see p. 25 and Figs. 74-75). 

In numbers of cases we have made use of open nomenclature in our specific and 
generic assignments. We have followed this method where either the preservation 
or numbers (or both) of specimens were so poor that we felt it unjustifiable to use a 
formal name, even though we have sometimes recognized particular forms as 
representing new species, and, in two cases, new genera. 

Ranges for species are given only for the Avon Gorge and North Crop, except 
where species are not present in these areas. Ranges for other areas are shown on 
the appropriate range charts. In all cases, the ranges represent the maximum 
distribution of the species, which may not always be present in every sample residue 
between its first and last appearance. In most such cases, its absence is attributable 
to particular samples proving barren or producing very low yields. 

Catalogue numbers refer to specimens deposited in the British Museum (Natural 
History). 

Genus ANGULODUS Huddle 1934 
1934 Angulodus Huddle : 76. 

Type species. Hindeodella walrathi Hibbard 1927. 

Angulodus walrathi (Hibbard) 
Plate 29, fig. 8 

1927 Hindeodella walrathi Hibbard : 205, text fig. 4a, b. 

1934 Angulodus walrathi (Hibbard) Huddle : 77, PI. 4, fig. 15 ; PI. 10, fig. 5. 

1934 Angulodus demissus Huddle : 77, PI. 10, fig. 15. 

1940 Angulodus elongatus Stauffer (partim) : 419, PI. 58, figs. 1, 2 only. 

non 1957 Angulodus walrathi (Hibbard) Bischoff : 17, PI. 5, figs. 44, 45. 

non 1961 Angulodus walrathi (Hibbard) Higgins : 10, fig. 16. 

Material. 21 specimens : figured, X 36. 

Range. North Crop KL 3-ZLA 6, Avon Gorge Z 4-Z 37. 

Description. An arched elongated unit, with a straight anterior bar which is 
laterally compressed and deflected through 45 ° in a vertical plane. The anterior 
bar bears a series of at least 6 fine, laterally compressed, confluent, posteriorly inclined 
denticles, their apices being discrete. The apical denticle is about twice as high and 
three times as wide as the other denticles, and is of the same general form. The 



BRITISH AVONIAN CONODONT FAUNAS 



67 



posterior bar is about three times longer than the anterior bar and up to twice as 
deep. The denticles are fine, laterally compressed, needle-like, fused for about half 
their length, and posteriorly inclined at about 60 ° to the horizontal in the anterior 
third. In the posterior portion, the inclination tends to increase, so that in the 
recurved posterior terminus of the bar, the denticles lie parallel to the main posterior 
bar. The denticles of the posterior bar tend to have a hindeodellid arrangement. 
The posterior bar bears up to 23 denticles, about 18 of which he anterior to the 
recurved posterior terminus. It has a straight aboral edge in the posterior two- 
thirds. The basal cavity is small and confined to the area immediately anterior to 
the apical denticle. 



Posterior bar 



Apical denticle 




Posterior pa 

of posterior 

or bar 

Anterior part 
of posterior bar 

Point of depression 

Fig. 17. Angulodus sp. showing morphological terms used in the text. 

Angulodus sp. nov. B 
Plate 29, figs. 5a, b 



8 specimens : figured, X 37. 
and horizon. North Crop, River Clydach, Nr. Gilwern, upper part 



Material. 

Locality 
of Lower Z Zone. Sample ZLA 14 

Range. North Crop ZLA 8-ZLA 14, Avon Gorge Z 34-C 7. 

Description. An Angulodus with robust bar, the short anterior portion being 
depressed and deflected. Posterior bar up to five times as long as anterior, with 90 ° 
posterior depression. Stout discrete denticles. 

The whole unit is robust. The bar bears rather rounded lateral faces, and lacks 
any conspicuous lateral compression. The unit is depressed downward at both the 



68 BRITISH AVONIAN CONODONT FAUNAS 

posterior and the anterior extremities. The apical denticle is of the same size as the 
denticles of the anterior bar. The anterior bar is short, depressed downward through 
70 ° and deflected inward up to 90 °. It bears isolated sub-circular denticles, which 
tend to increase in size anteriorly. The posterior bar is about four to five times as 
long as the anterior bar. It is deflected through about 90 ° at its posterior termina- 
tion, and bears irregular, isolated, sub-circular denticles, which increase in size 
posteriorly to the point of depression, when they decrease in size towards the 
posterior end. Those in the anterior portion of the posterior bar bear smaller 
denticles (about one third the width of the larger ones) between them. In aboral 
view the unit is excavated beneath the apical denticle and possesses an inverted basal 
cavity over its whole length. Here and elsewhere " inverted " is used to describe a 
basal cavity with wide flaring opening and more or less restricted internal form (see 
Lindstrom 1964). This is visible as a basal flange in lateral view. 

Angulodus sp. nov. C 
Plate 29, figs. 3a~4c 

Material. 18 specimens : figured, X 38, X 39. 

Locality and horizon. North Crop, River Clydach, Nr. Gilwern, K and Lower 
Z Zones. Sample ZLA 10. 

Range. North Crop KL i-ZLA 14, Avon Gorge Z 34-Z 38. 

Description. A simple, stout, short unit, with a few stout, isolated denticles ; 
bars are deflected and depressed in at least two directions on the inner side. 

The apical denticle is relatively small, sub-circular in cross-section, posteriorly 
inclined and continuously curved at various angles towards the inner side. The 
short, stout anterior bar is deflected through 90 ° and then depressed downward 
through 90 °. It bears 3 to 4 massive, discrete, sub-circular denticles, which tend to 
decrease in size distally. The posterior bar is massive and very short, the anterior 
portion being about equal in length to the anterior bar and only slightly longer than 
the posterior portion. It is stout, with broadly convex lateral faces, and is slightly 
twisted. The posterior depression may be strong or gentle, but the distal end is 
depressed through about 90° in both cases. It bears only 3 to 5 stout, sub-circular, 
posteriorly inclined, isolated denticles, the largest being at the point of depression. 

In aboral view the unit is expanded, the cavity being large and extremely shallow, 
in some cases approaching an inverted basal cavity ; it is largely confined to the 
anterior portion of the posterior bar (PI. 29, fig. 3c). 

Remarks. This is a very unusual form, the only comparable species being 
Centrognathodus spurius Branson & Mehl (1934 : 198). The present specimens differ 
from this in the relative position of the basal cavity and the lack of an " outer spur ". 
A form described as Angulodus demissus Huddle by Bischoff & Ziegler (1957 : 43) is 
also similar. This latter form, which is not Angulodus demissus Huddle, could be 
the same as our specimens. Angulodus sp. C differs from Angulodus sp. D in the 
nature of the posterior termination. 



BRITISH AVONIAN CONODONT FAUNAS 69 

Angulodus sp. nov. D 
Plate 29, figs. ia-2c 

Material, io specimens : figured, X 40, X 41. 

Locality and horizon. North Crop, River Clydach, Nr. Gilwern, upper part of 
Lower Z Zone. Sample ZLA 11. 

Range. North Crop ZLA 8-ZLA 14, Avon Gorge Z 34-Z 38. 

Description. A simple bar unit similar to Angulodus sp. C but with a longer 
anterior portion of the posterior bar and a less marked and distinctly denticulated 
depression of the posterior termination. 

The apical denticle is fairly small, sub-circular in cross-section, inclined posteriorly 
and towards the inner side, so that it does not lie in the same plane as the other 
denticles or the rest of the unit. The anterior bar is short, massive, deflected 
through 90° ; horizontal or feebly arched upward and then depressed through 90 °. 
It commonly bears 4 to 5 stout, irregular, isolated, sub-circular denticles, which tend 
to be tallest in the anterior part. The anterior part of the posterior bar is one and a 
half to twice as long as the anterior bar. The oral surface bears 3 to 4 discrete 
pointed denticles, their diameter being about two thirds that of the apical denticle, 
and their cross-sections sub-circular to biconvex. They are inclined at about 45 ° to 
the posterior bar, and are separated by irregular smaller " hindeodellid " denticles. 
They tend to decrease in size posteriorly towards the point of depression. The 
posterior part of the posterior bar is depressed at an angle of 90 °. It is very short, 
and its oral surface is limited to a single, large, fang-like denticle. This is strongly 
laterally compressed, with flat to gently convex lateral faces, and anterior and 
posterior edges. It lies almost parallel to the anterior part of the posterior bar. 
The posterior termination of the unit is pointed to sharply spatulate. A minute 
secondary denticle may be developed on the posterior edge of the most posterior 
denticle. The basal cavity is confined to the area below the apical denticle. The 
posterior bar commonly has a very fine aboral keel along its whole length. 

In aboral view the sub-apical pit is large and extremely shallow, approaching the 
form of an inverted basal cavity. 

Remarks. A form similar to this species is described by Bischoff & Ziegler 
(1957 : 43, PL 20, figs. 3, 6) as Angulodus gravis Huddle. The holotype of A. gravis 
differs greatly from the specimens figured by Bischoff & Ziegler, but there is a marked 
similarity between their forms and the present specimens. 

Genus APATOGNATHUS Branson & Mehl 1934 
1934 Apatognathus Branson & Mehl : 201. 

Type species. Apatognathus varians Branson & Mehl 1934 

Apatognathus bladus sp. nov. 
Plate 20, figs. I5a-i6b 

Derivation of name. From Latin blade. 



70 BRITISH AVONIAN CONODONT FAUNAS 

Diagnosis. Apatognathus in which denticles on anterior bar and apical denticle 
have very conspicuous anterior and posterior keels developed on edges. They are 
unusually wide and blade-like. Two largest denticles of anterior bar separated by 
single denticle from apical denticle. Denticles of posterior bar adjacent to apical 
denticle are minute. Whole unit sharply depressed at apex and strongly inwardly 
twisted. Inner lateral faces of both bars bear conspicuous ridges near point of 
contact with denticles and are flat to concave below these ridges. 

Material. 8 specimens : Holotype X 45, Paratype X 46 (both figured). 

Type locality and horizon. North Crop, Craig-y-dinas, Breconshire. Sample 
CYD 7. 

Range. North Crop CYD 7. 

Description. Anterior bar of unknown length ; it is deep and thin, bearing 
more than 4 strong, greatly laterally compressed denticles on its oral surface, the 
largest two being separated from the apical denticle by a single small denticle. 
The denticles of the anterior bar, as well as the apical denticle, are so strongly lat- 
erally compressed that they have strong lateral keels developed on their anterior and 
posterior edges. The combined width of these keels equals or exceeds the width of 
the "core" of the denticles. The denticles are basally confluent but are discrete for 
most of their lengths. They are inclined slightly posteriorly. Below the base of 
these denticles the apical bar bears a conspicuous longitudinal ledge which is rounded 
and parallels the oral surface of the bar. Below this ledge the aboral surface is 
relatively wide and there is a slight ledge developed on its inner lateral face. It is not 
conspicuously excavated. The apical denticle is strongly biconvex in cross-section 
but the anterior and posterior edges are conspicuous features on both margins. It is 
elongated, but is not conspicuously greater in width than the largest denticle on the 
anterior bar. It is straight and tapers gradually. The posterior bar is only about 
one-third the depth of the anterior, but it is thicker than it is deep. Its oral surface 
bears a series of crowded, minute and more or less sharply pointed denticles. In 
cross-section the posterior bar is more or less quadrate with a sharp longitudinal 
ridge developed on the upper inner lateral face and a more or less smooth to flat outer 
lateral face. Its basal surface is the widest part of the bar and is flat. In outer 



Posterior bar 




Apical denticle 



Outer face 



Twisted distally 



Anterior bar 
Inner face 



Fig. 18. Apatognathus sp. showing morphological terms used in the text. 



BRITISH AVONIAN CONODONT FAUNAS 71 

lateral view the lateral walls of the bar and the denticle faces are flat, and the whole 
unit is continuously recurved so that all denticles point inward. The slight lateral 
flange on the outer aboral lateral face of the anterior bar and the wide posterior 
aboral surface are conspicuous features. 

Remarks. Although our specimens are fragmentary the distinctive size and 
character of the denticles, as well as the form of the base, appear to set this species 
apart from all those previously described. 

Apatognathus chauliodus Varker 
Plate 20, figs, ia, b, ; 2a, b 
1967 Apatognathus ? chaulioda Varker : 129, 131, PI. 17, figs. 1-3, 5. 

Material. 2 specimens : figured, X 44, X 550. 

Range. Avon Gorge D 7. 

Description. The bars diverge at an angle of 25°-35° and in inner lateral view 
are inclined inwards to slightly face one another. The apical denticle is as wide as 
the prominent bar cusps, widest at its base and sharply pointed. It is slightly 
curved and inclined to the posterior. A prominent denticle is present on each of the 
lateral bars. These bar cusps are equal in size to the apical denticle, but are 
separated from it by up to 5, but commonly 2 or 3, small compressed denticles, 
which are shorter in length than the depth of the bar and are fused with one another. 
The denticles of the bar adapical to the bar cusp may be longer than the height of the 
bar, and are discrete. The aboral edge of the bar is straight, but the bar itself 
increases in depth towards the apex from its shortest depth at the adapical extremity. 
The bar denticles are slightly inclined inwards. The aboral edge of the bars is sharp, 
an aboral groove is present and the basal cavity beneath the apical denticle is 
circular. 

Apatognathus geminus (Hinde) 
Plate 20, figs. 3a-4b, 6a~7b 

1900 Prioniodus geminus Hinde : 344, PI. 10, fig. 25. 
1928 Prioniodina ? gemina (Hinde) Holmes : 19, PL 5, fig. 10. 
i960 Apatognathus geminus (Hinde) Clarke : 4, PI. 1, figs. 1, 2. 

1963 non Apatognathus ? gemina (Hinde) Rexroad & Collinson : 7, PI. 1, figs. 12-17. 
( = Apatognathus scalena Varker). 

Material. 4 specimens : figured, X 54, X 55, X 56, X 57. 

Range. North Crop CYD 6-3D 14/15, Avon Gorge C 16. 

Description. The most distinctive features of this species are the prominent 
apical denticle and the large size of two denticles on the anterior bar adjacent to that 
denticle. The whole unit is strongly recurved and strongly laterally flexed, so that 
in outer lateral view the aboral surface is visible along almost the whole length of the 
unit. Both bars are strongly flexed inwards so that the denticles appear to radiate 



72 BRITISH AVONIAN CONODONT FAUNAS 

away from the apical junction. The anterior bar is relatively short and straight with 
a flat outer lateral face. It bears up to 7 denticles, not including the apical denticle, 
and these are basally confluent but apically discrete. Their outer lateral faces are 
strongly convex and they have sharp anterior and posterior edges and they decrease 
in size towards the anterior tip. The apical denticle is about twice as long as the 
largest of the denticles of the anterior bar. It is inclined posteriorly and is paralleled 
by the denticles of the anterior bar ; it is straight with a very strongly convex outer 
lateral face and sharp anterior and posterior edges ; it is not expanded on the outer 
aboral margin. The posterior bar is very slightly shorter than the anterior, and its 
denticles are conspicuously smaller ; they are of more or less subequal height and 
they are about 7 in number. They are basally confluent but apically discrete with 
sharp anterior and posterior edges and feebly to gently convex outer lateral faces ; 
these are less conspicuously convex than the faces of the anterior denticles ; on 
the outer lateral aboral margin of the posterior bar there is a more or less con- 
spicuous longitudinal ridge developed parallel to the base. We take this to be the 
" laterally tumid " character referred to by Clarke (i960). The angle of divergence 
of the two bars when viewed from the outer lateral side is about 30°-40° ; they 
are also strongly flexed inwardly and join each other at an angle of about 40 ° in the 
inner lateral view, in such a way that the denticles of the posterior bar are erect and 
those of the anterior bar point outwards towards the observer. The bars are strongly 
flexed inward and the denticles curve inward, as well as posteriorly ; the denticles 
of the posterior bar are inclined anteriorly and tend to parallel the main denticle. 
The inner lateral faces of both the anterior and posterior bars are flat and a rather 
bevelled aboral edge is developed from them, excavated throughout its length by a 
narrow, slit-like cavity, which does not increase markedly in size below the apical 
denticle. 

Remarks. Clarke's illustration of Hinde's specimens makes it clear that the 
characteristics of the species are the relatively larger size of the denticles adjacent to 
the apical denticle, and the almost platform-like lateral edges developed on the 
posterior bar. 

Apatognathus petilus Varker 
Plate 20, figs. I2a-i4b; 17a, b 
1967 Apatognathus petila Varker : 135, 136, PI. 17, fig. 11, PI. 18, figs. 7, 10, 11. 

Material. 23 specimens : figured, X 50, X 51, X 52, X 53. 

Range. North Crop CYD 7-3D 14/15, Avon Gorge C 7-C 16, D 7. 

Description. The orientation of these units is arbitrarily defined by regarding 
the longer bar as posterior, although the inclination of the apical denticles does not 
always justify this. Apatognathus with slender elongated lateral bars continuously 
and strongly recurved and flexed ; apex of arch formed by them marked by develop- 
ment of 5 large denticles, of which three medial are largest but no single apical 
denticle is conspicuously larger than rest. 



BRITISH AVONIAN CONODONT FAUNAS 73 

The dental units are slender with a straight, elongated, posterior bar. The 
posterior bar is about one third longer than the anterior, and has 17-24 crowded 
denticles, their apices being sharply to bluntly pointed but discrete ; they tend to be 
more or less uniform in size, though those near the distal end of the bar are slightly 
smaller than the rest of the series. The inner lateral face of the bar is flat and the 
base of the aboral edge of the bar when seen in lateral view is straight or very feebly 
convex. 

The posterior bar makes an angle of about 45 ° with the anterior when seen in 
lateral view : the posterior bar itself is slightly flexed inwards, although both the 
distal and proximal thirds are more or less straight. 

The anterior bar is shorter than the posterior, and its aboral edge is conspicuously 
straight. In lateral view it bears a series of crowded denticles which are confluent 
at their bases but apically discrete, and which have bluntly pointed free tips ; they 
number up to twelve and increase more or less steadily in size towards the apex. 
The apex is rounded on the aboral margin and is marked by the development of five 
rather large and conspicuous denticles, of which the three medial ones are the largest. 
They are curved inward and sometimes slightly posteriorly, but in most specimens 
they are more or less erect. They are basally confluent but apically discrete and are 
biconvex in cross-section, with sharp anterior and posterior edges, and gently convex 
lateral faces. The largest denticles tend to be large and conspicuous and, when 
viewed laterally, they tend to radiate from the apex of the arch. There is a slight 
tendency for the denticles of the posterior bar to increase in size apically. The 
whole inner lateral face of the unit is continuously recurved, although at any one 
point on the face the denticles tend to have a flat to only feebly concave surface. In 
outer lateral view the surface is feebly convex to flat and the aboral margin is marked 
by a more or less conspicuous ridge, developed on the outer lateral face. The whole 
aboral cavity is excavated below the apex. 

Remarks. The distinctive features of this species are the general form and 
curvature of the anterior and posterior bars and the development of the apical 
denticulation, in which a series of denticles, rather than any individual denticle, are 
of major size. 

Apatognathus porcatus (Hinde) 
Plate 31, fig. 27 

1900 Prioniodus porcatus Hinde : 344, PI. 10, fig. 26. 

1928 Prioniodus porcatus Hinde ; Holmes : 22, PI. 3, fig. 26. 

i960 Apatognathus porcata (Hinde) Clarke : 5, PI. 1, figs. 3, 4. 

1963 non Apatognathus ? porcata (Hinde) Rexroad & Collinson : 8, PI. 1, figs. 7— 11. 

Material, io specimens : figured, X 220. 

Range. North Crop CYD 6-7, Avon Gorge C 9-C 16. 

Description. Clarke's diagnosis of this species, as well as his illustration of 
Hinde's holotype, make it clear that its distinctive features are the relatively uniform 
size of the denticles, and the very strong bilateral extension of the oral surface of the 



74 BRITISH AVONIAN CONODONT FAUNAS 

anterior bar. This is well shown by the view of the specimen illustrated on PI. i, 
fig. 4 of Clarke. It seems, therefore, that the specimens described by Rexroad and 
Collinson must be excluded from the species, for in them the anterior bar does not 
appear strongly laterally expanded. Material from both Scotland and the North 
Crop representing this species is fragmentary but the anterior bar shows the charac- 
teristic very strong lateral expansion. 



Apatognathus scalenus Varker 
Plate 20, figs. o,a-nb 

1963 Apatognathus ? gemina (Hinde) Rexroad & Collinson : 8-9, PI. 1, figs. 12-17. 
1967 Apatognathus ? scalena Varker : 136, 137, PI. 18, figs. 1, 2, 4, 5. 

Material. 10 specimens : figured, X 47, X 48, X 49. 
Range. North Crop CYD 6-3D 14/15. 

Description. The characteristic features of this species are the strong lateral 
flexing of the anterior bar, the general form of the unit, the development of a strong, 
elongate, laterally compressed denticle at the apex, an apical angle of about 30° in 
lateral view, and the development of at least one strong denticle in the medial portion 
of the posterior bar. 

Varker has given a detailed description of this species. The anterior bar is about 
equal in length to or slightly longer than the posterior. It bears 10-14 laterally 
compressed, pointed, sharp edged, basally confluent, inwardly curving denticles, 
which increase in size proximally. The apical denticle is at least two to three times 
as long as the largest of the remaining denticles ; it has sharp anterior and posterior 
margins and a convex inner lateral face, the convexity decreasing distally. The 
posterior bar develops about 10 denticles, of which the one in the medial position is 
twice as large as its neighbours and slightly larger than that adjacent to the apical 
denticle. These denticles are rather less closely spaced than those of the anterior 
bar, and in some of them even the basal surfaces are discrete ; they are sharply 
pointed and stand more or less erect to the bar, but those nearest the apical denticle 
are recurved so that they lie more or less parallel to it. The lateral faces of both bars 
are marked on the inner side by a more or less conspicuous shoulder below the origin 
of the denticles. 

Both bars are twisted laterally and they diverge when viewed orally at an angle of 
about 30 °, as well as being twisted in a horizontal plane, so that in oral view all the 
denticles radiate away from the apical area. 

In outer lateral view a conspicuous longitudinal ridge is developed at about mid- 
height. In both bars the aboral surface is excavated by a narrow slit-like groove, 
which is only slightly expanded below the apical denticle. 

Remarks. In some specimens the posterior bar is marked by the development 
of two conspicuously large denticles, although one of these is always larger than the 
other. 



BRITISH AVONIAN CONODONT FAUNAS 75 

Apatognathus varians Branson & Mehl 
Plate 20, figs. 5a, b 

1934 Apatognathus varians Branson & Mehl : 201, PL 17, figs. 1-3. 
non 1939 Apatognathus ? varians Branson & Mehl ; Cooper : 385, PI. 47, fig. 30. 

1944 Apatognathus varians Branson & Mehl ; Branson & Mehl in Shimer & Shrock : 402, 

PI. 93, figs. 59-61. 
1956 Apatognathus varians Branson & Mehl ; Bischoff & Ziegler : 145, PI. 14, fig. 3. 
1958 Apatognathus varians Branson & Mehl ; Klapper : 1085, PI. 141, figs. 6, 8. 
1961 Apatognathus varians Branson & Mehl ; Ethington, Furnish & Wingert : 763, 

PI. 90, fig. 11. 
1961 Apatognathus varians Branson & Mehl ; Freyer : 36, PI. 1, fig. 13. 
1965 Apatognathus varians Branson & Mehl ; Spasov : 84, PI. 1, fig. 3. 
1965 Apatognathus varians Branson & Mehl ; Ethington : 575. 

Material. 6 specimens : figured X 42. 
Range. North Crop ZLA g-ZL 9. 

Description. The unit is considerably arched and bowed. The apical denticle 
is laterally compressed, with convex lateral faces, and sharp anterior and posterior 
edges. It is inclined posteriorly and laterally towards the inner side. The anterior 
bar lies in the same plane as the apical denticle, but is twisted inwards distally. It 
bears at least 20 closely crowded, sub-circular, posteriorly-inclined denticles, their 
apices being discrete and pointed. 

The anterior bar is strongly laterally compressed in its distal third, with flattened 
lateral faces, but the inner and outer lateral faces become strongly convex in their 
proximal two-thirds. The posterior bar is short, considerably flexed, about as long 
as that of the anterior and makes an angle of about 20° with the anterior bar. It is 
curved inward, and bears denticles similar to those of the anterior bar, but tending 
to be upright or anteriorly inclined. Both bars decrease in height towards their 
distal extremities. The basal cavity is minute and situated beneath the apical 
denticle. 

On specimen number X 42 (Plate 20, figs. 5a, b) the inner lateral face of the apical 
denticle tends to be flat, but the outer lateral face is strongly convex, the inner lateral 
face of the bars immediately below the apical denticle tending to be rather flattened. 
The two denticles immediately posterior to the apical denticle tend to be larger than 
any of those on the anterior bar. The distal portion of the posterior bar is broken. 
The outer lateral face of the anterior bar is similar in general cross-section to the 
inner lateral face. 

Apatognathus cf. libratus Varker 
Plate 20, figs. 8a, b 
1967 Apatognathus ? librata Varker : 134, 135, PL 18, figs. 3, 6, 8, 9, 12, 13. 
Material, i specimen : figured, X 58. 
Range. Scotland DUN 78. 
Description. The characteristic feature of this species is its virtual bilateral 



76 BRITISH AVONIAN CONODONT FAUNAS 

symmetry. In the present specimen the two limbs diverge at an angle of about 45 ° 
in outer lateral view. The denticles stand more or less erect to the limbs towards 
their distal extremities but they tend to radiate away from the apex ; they are 
more or less sub-equal in size and closely similar in size on both anterior and posterior 
bars. The apical denticle tends to be only slightly larger than the largest on the 
bars, on which the largest denticles tend to be separated by a single denticle from 
both the anterior and posterior edges of the apical denticle. The denticles are 
confluent for about two-thirds of their length, with sharp anterior and posterior 
edges and gently convex lateral faces. The whole unit is continuously recurved 
inward and on both the anterior and posterior limbs there is a more or less con- 
spicuous basal longitudinal ridge developed near the aboral margin. In inner lateral 
view the whole unit is regularly and continuously concave. The bars of the present 
specimens are of rather unequal length, the anterior bearing 9 denticles and the 
posterior 8 ; it is probable that neither is complete, however. 

Remarks. The present specimen bears a very close resemblance to Varker's 
holotype in all features except the relative size of the apical denticle. In the present 
specimen this is only about half the size of that in Varker's specimens. This does 
not seem to us, at present, a valid reason for regarding the two forms as distinct 
species. Varker notes that the processes of his specimens bear up to 20 or more 
denticles. 

We have used the name of this species as the zonal name for one of our zones. 
The zone is characterized by the common occurrence of apatognathids, virtually all 
of which are broken, however. Many of these resemble the present species, but they 
are too fragmentary to include in the count of material. 

Apatognathus sp. nov. A 
Plate 31, fig. 22 

Material. 2 specimens : figured, X 43. 

Type locality and horizon. North Crop, River Clydach, Nr. Gilwern, Z Zone. 
Sample ZLA 13. 

Range. North Crop ZLA 13. 

Description. A strongly arched Apatognathus with conspicuous apical denticle. 
Slender recurved anterior bar has about 10 crowded denticles, and is curved in the 
same plane as the apical denticle. Posterior bar stout, deep, deflected and depressed, 
with 4-5 large, discrete denticles. 

The unit is arched and bowed. The apical denticle is tall, laterally compressed, 
with knife edges on the anterior and posterior margins, posteriorly recurved and 
laterally inclined toward the inner side. The outer face is strongly, and the inner 
face feebly, convex. The anterior bar lies in the same plane as the apical denticle 
and is shallow and somewhat recurved. It bears about 10 laterally compressed, 
posteriorly inclined, partially fused denticles. The deep posterior bar is deflected, 
and depressed. It bears a series of 4 or 5 large, discrete, laterally compressed 



BRITISH AVONIAN CONODONT FAUNAS 77 

denticles, standing perpendicular to the bar, the largest developed at about midpoint. 
The basal cavity is minute and is situated beneath the apical denticle. 

Remarks. This form is very similar to Apatognathus} geminus (Hinde) of Rexroad 
and Collinson (1963), our specimens differing only in that the posterior bar is more 
strongly curved and twisted. This may not be specifically significant, and if the two 
forms are identical, the range of the present form would be extended upward, into the 
St. Louis Formation of the Upper Mississippi Valley. Rexroad and Collinson 
(1963 : 7) point out that in North America there is a gap between the Upper 
Devonian and Upper Visean record of Apatognathus. Our apatognathid fauna 
appears to bridge that gap, and thus Apatognathus may not necessarily be a poly- 
phyletic genus as Rexroad and Collinson suggest. 

Apatognathus sp. 

Plate 31, fig. 2 

Material. 16 specimens : figured, X 318. 

Range. Avon Gorge Z 36-D 32. 

Description. Fragmentary apatognathids occur in various parts of the succes- 
sion. The specimen illustrated represents one such form, though other broken 
specimens show considerable variation. They are not sufficiently complete to make 
it possible to refer them to individual species. 

Genus CAVUSGNATHUS Harris & Hollingsworth 1933 
1933 Cavusgnathus Harris & Hollingsworth : 200-201. 
Type species. Cavusgnathus alta Harris and Hollingsworth 1933. 

Description. Harris and Hollingsworth (1933) gave the following description 
for the genus : 'This genus is erected to include those lanceolate plated conodonts 
with no semblance of a median crest in the median oral channel. Outline of plate 
lanceolate to claviform ; oral face of plate with complete, deep, median longitudinal 
channel without crest and bordered by marginal rims ornamented with denticles, 
nodes, corrugations, or combinations of the same ; posterior bar denticulate'. 

Ellison (1941) gave the following revised description : 'Elongate platform-like 
teeth with high sides, extending parapet-like above a median longitudinal trench, 
one parapet continued into a free longitudinal blade and connected at the posterior 
end to opposite parapet, whose length is limited by the length of the platform ; 
aboral surface of platform smooth, deeply excavated as a longitudinally elongate, 
laterally asymmetrical spathodid-like cup, pointed at each end, transversed by a 
median longitudinal groove, which extends to the ends of the platform and along the 
aboral edge of blade ; sides of platform somewhat constricted laterally above the 
aboral margin, to produce a lip-like lateral margin of variable width ; oral surface of 
platform more or less grooved transversely, oral edge of blade denticulate and 
crenulate. 



78 



BRITISH AVONIAN CONODONT FAUNAS 



For purposes of description, the blade is directed anteriorly. It is continued 
posteriorly as the outer edge of platform, the blade parapet. The elevated inner edge 
of the platform is the inner parapet.' 

Remarks. Cavusgnathus bears a marked resemblance to the genus Mestognathus, 
but the two are easily distinguished on the basis of their basal cavities, that of 
Mestognathus being small and narrow and that of Cavusgnathus wide and flaring. 

The anterior blade in the cavusgnathid group has hitherto been thought to be 
confined to the outer side of the unit and to be lateral in position (Rexroad in 
Lindstrom 1964 : 124). However, the present study has shown that the position 
of the blade in Cavusgnathus varies through the section. In the K Zone it is both 
medial and lateral in position, whereas in the Z to D Zones it is lateral in position. 
Some forms in the Z Zone have been found with the blade on the inner side. 

In North America it has hitherto been thought that Cavusgnathus developed from 
Taphrognathus in the Late Valmeyeran (Rexroad and Collinson 1963). Cavus- 
gnathus, however, makes its first appearance in the Avon Gorge in the basal beds of 



Platform 



Anterior — 




— Posterior 



Abora I edge 



Inner lateral view 



Basal 
cavity 




Outer side 




Oral surface 



Lot erol 

ridges 



Carino 



Aboral view 



Orol view 



Fig. 19. Cavusgnathus sp. showing morphological terms used in the text. 



BRITISH AVONIAN CONODONT FAUNAS 79 

the Z Zone and an earlier origin must therefore be suggested. The writers believe 
that Cavusgnathns may have had its origin in Spathognathodus plumulus sp. nov. 

Cavusgnathus charactus Rexroad 

Plate 13, figs. 6a~7d, I3a-c 

1957 Cavusgnathus characta Rexroad : 15-16, PL 1, figs. 1, 2. 

1961 Cavusgnathus characta Rexroad ; Rexroad & Collinson : PL 1. 

1963 Cavusgnathus characta Rexroad ; Rexroad & Collinson : 8, PL i, fig. 29. 

Material. 8 specimens : figured, X 59, X 61, X 62. 
Range. North Crop CYD 7, Avon Gorge S 5-S 44. 

Description. The diagnostic characters of this species are the general form of the 
anterior blade, which consists of six to eight denticles with low rounded apices of 
more or less uniform size, except for those in the anterior portion. The posterior end 
of the blade is separated by a distinct undenticulated depression from the outer 
lateral face of the posterior platform. The free anterior blade is not long in com- 
parison with the length of the platform. In outer lateral view the platform decreases 
in depth towards the posterior end. Its oral surface is bluntly crenulate and the 
whole aboral surface of the unit is regularly concave. There is a conspicuous 
thickening below the basal cavity, which is situated in the anterior portion of the 
platform and the whole outer lateral edge of the blade is bevelled. In some speci- 
mens there are only four or five denticles on the anterior blade, the most posterior 
being the largest and most massive. They all stand more or less erect to the bar. 
The oral margin of the platform is continuously convex in outer lateral view, the 
outer parapet obscuring the inner, when seen in this direction. The blade tends to 
decrease in depth posteriorly ; its anterior aboral corner is bluntly rounded. In 
inner lateral view the basal cavity makes a conspicuous flaring feature on the aboral 
surface, and the oral edge of the platform is strongly convex and irregularly crenulate. 
The platform tends to show some narrowing anteriorly and its widest point is in the 
posterior half. In the posterior half there is a median carina of variable length, 
consisting of a number of rather conspicuous but fused, strongly laterally compressed 
nodes. The carina extends beyond the posterior limit of the platform proper. The 
platform edges are decorated with feeble transverse ridges and the whole median area 
of the platform is excavated by a deep U-shaped trough, which runs parallel to the 
anterior blade and does not decrease greatly in depth when traced anteriorly. 

In aboral view the aboral cavity is widely flaring and asymmetrical, but the basal 
pit itself is restricted to the anterior quarter of the platform. It is deep but not very 
broad and is extended as a longitudinal slit to the posterior end of the unit, the 
lateral edges of the lip gradually converging towards the posterior end. It is also 
extended anteriorly for a short distance, though the inner lateral lip, when seen in 
aboral view tends to be more widely flared than the outer, and also in some, though 
not in all, specimens to extend further forward. 

The total length of the blade is about one-third of the whole length of the unit. 
The blade is free for about half its length. 



8o 



BRITISH AVONIAN CONODONT FAUNAS 



Remarks. In some specimens there is a slight asymmetry of the posterior 
platform, the inner lateral posterior margin tending to be more strongly outflexed 
than the outer. The platform is widest on its oral edge and, especially in its posterior 
half, tapers rapidly towards its aboral margin. 

Cavusgnathus convexus Rexroad 
Plate 14, figs. 2a-d 



1957 Cavusgnathus convexa Rexroad 

1958 Cavusgnathus convexa Rexroad 
1 961 Cavusgnathus convexa Rexroad 

1964 Cavusgnathus convexa Rexroad 

1965 Cavusgnathus convexa Rexroad 



17, PI. 1, figs. 3-6. 

Rexroad : 16, PI. 1, figs. 12-14. 

Rexroad & Collinson : PI. 1. 

Rexroad & Furnish : 670, PI. 111, fig. 1. 

Rexroad & Nicoll : 17, PI. 1, figs. 14, 15. 



Material. 5 specimens : figured, X 63. 

Range. Avon Gorge S 20-S 41, North Crop 3D 13. 

Description. The margins of the inner and outer parapet are straight. A deep 
trough runs the length of the platform and occasionally a few nodes form a carina at 
its posterior extremity. The parapets are ornamented by regularly spaced, trans- 
verse ridges. In lateral view, the anterior blade is seen to consist of six laterally 
compressed denticles, which are fused nearly to their apices. The anterior blade is 
highest near, but not at, its posterior extremity and this gives the blade a convex 
oral edge. The anterior blade, which is less than one third the total length of the 
unit, is free for half its length. The oral edge is convex and the aboral edge is 
straight to slightly arched. The posterior edge is rounded. The basal cavity is of 
moderate depth and asymmetrical ; it is long, extending for two thirds the length of 
the unit, and reaches the posterior extremity of the unit. The inner is more flared 
than the outer. A keel runs from the anterior edge of the basal cavity to the 
anterior extremity of the unit. 



Cavusgnathus cristatus Branson & Mehl 
Plate 14, figs. 3a-d 



1940 Cavusgnathus cristata Branson & Mehl : 
1947 Cavusgnathus cristata Branson & Mehl ; 

(non PI. 20, figs. 7-10). 
1953 Cavusgnathus cristata Branson & Mehl ; 
1956 Cavusgnathus cristata Branson & Mehl ; 

1956 Cavusgnathus cristata var. grandis Elias : 

1957 Cavusgnathus cristata Branson & Mehl 
naviculus.) 

1958 Cavusgnathus cristata Branson & Mehl 
1 96 1 Cavusgnathus cristata Branson & Mehl 
1 96 1 Cavusgnathus cristata Branson & Mehl 



177, PI. 5, figs. 26-31. 
Cooper (partim) : 91, 



PI. 20, figs. 4-6 



Hass : 77, PI. 14, figs. 12 
Elias : 115, PI. 11, figs. 1 
115, PI. 11, figs. 12-14. 
; Bischoff : 19, PI 



-14. 
-6. 



2, figs. 7a, b. 



[ = C. 



Rexroad : 16, PI. 1, 
Rexroad & Burton : 
Rexroad & Collinson 



figs. 15-17- 
1151, PI. 138, fig.16. 
: PI. 1. 



Material. 8 specimens : figured, X 64. 

Range. Avon Gorge D 26, North Crop 3D 14/15-3D 22. 



BRITISH AVONIAN CONODONT FAUNAS 81 

Description. The margin of the outer parapet of the platform is straight and 
that of the inner parapet, convex. A deep trough is developed for the greater part 
of the length of the platform, except for the posterior quarter of the platform, where 
there is a short carina, which bears a few nodes. The platform is ornamented by a 
number of transverse ridges of medium length, which extend into the trough. In 
oral view the flaring of the basal cavity on its inner side is seen. 

The anterior blade, which rises out of the outer parapet, slopes slightly towards the 
anterior. The posterior three denticles of the anterior blade are highest. The 
anterior edge of the anterior blade and the posterior edge of the platform are of equal 
elevation. Half the length of the anterior blade is free. Aborally, the basal cavity is 
asymmetrical and flared, there being a greater flare on the inner side than on the 
outer. 

Remarks. This species closely resembles Cavusgnathus convexus but differs from 
the latter in that the basal cavity does not extend to the posterior extremity of the 
unit. In addition C. convexus rarely bears a carina and has fewer and shorter ridges 
in the surface ornamentation. 

The present specimens show an even closer similarity to C. regularis Youngquist & 
Miller (as interpreted by Rexroad & Nicoll 1965, PI. 1, figs. 16, 17) and this species 
may be a junior synonym of C. cristatus Branson & Mehl. 

Cavusgnathus naviculus (Hinde) 
Plate 13, figs. I2a-d. Plate 14, figs, ia-d, 4a-6d 

1900 Polygnathus navicula Hinde : 342, PL 9, fig. 5. 

1928 Polygnathus navicula Hinde ; Holmes : 18, PL 7, fig. 14. 

1947 Cavusgnathus cristata Branson & Mehl ; Cooper (partim) : 91, PL 20, figs. 7-10. 

J 957 Cavusgnathus cristata Branson & Mehl ; Bischoff : 19, PL 2, figs. 7a, b. 

i960 Cavusgnathus navicula (Hinde) Clarke : 23, PL 4, figs. 1-3. 

i960 Cavusgnathus inflexa Clarke : 23, PL 3, figs. 17, 19. 

1961 Cavusgnathus navicula (Hinde) Rexroad & Burton : 1151, PL 139, figs. 4-13. 

1965 Cavusgnathus navicula (Hinde) Rexroad & Nicoll : 17, 18, PL 1, figs. 24, 25. 

Material. 9 specimens : figured, X 65, X 66, X 67, X 68, X 69. 

Range. North Crop 3D 22, Avon Gorge D 26. 

Description. Unit slender and elongate in lateral view with short blade ; 
long, tapering inner and outer lateral sides which are almost straight in oral view, 
and are about two to three times as long as the blade. In oral view they are abruptly 
tapered in their posterior quarter, and the lateral edges are finely serrated. The oral 
surface is decorated by transverse lateral ridges, which converge, but do not meet, 
towards the narrow, shallow central trough. This trough is deepest in the anterior 
third ; on the inner lateral oral surface the ridges are obsolescent and are replaced 
by rounded nodes. There are about 10 transverse ridges on the outer lateral face. 
In the posterior third of the unit there is the development of a rather inconspicuous 
carina, consisting of fine, elongate, node-like denticles joined by a thin median ridge. 
The inner lateral aboral flange is conspicuous in oral view. 



82 BRITISH AVONIAN CONODONT FAUNAS 

In outer lateral view the unit is characterized by a rather straight median portion 
of more or less even depth, both the oral surface and to a lesser extent the aboral 
surface appearing straight-edged in lateral view. The basal apron of the outer 
lateral margin is considerably less flared and deep than that on the opposite lateral 
margin. 

The anterior blade decreases rapidly in depth anteriorly and its aboral edge, though 
straight, is depressed vertically. It bears about six oral denticles, of which only 
the most posterior are conspicuous, the largest being the most posterior of the 
series. The oral edge is bluntly crenulate and the whole outer lateral face is gently 
convex or flat, the junction with the aboral edge below the main denticle being 
concave. The posterior end of the unit is gently downflexed and the posterior aboral 
terminus is bluntly spatulate in lateral view. 

The posterior platform decreases in width towards the posterior end, the decrease 
being especially prominent in its posterior quarter. The anterior edge of the 
anterior blade falls sharply away in its anterior third, so that the anterior is vertical, 
but is still minutely denticulate. In inner lateral view the most prominent feature 
is the large, rounded, depressed apron above the aboral margin of the cavity. This 
occupies about half the total length of the unit and is regularly and strongly convex. 

In aboral view the cavity is also a conspicuous feature. The anterior half is wider 
than the posterior, the anterior point of origin being below the apical denticle. The 
point of maximum width is about one-third of the total length from the anterior end 
and the cavity is terminated posteriorly about five-sixths of the total length of the 
unit from the anterior end, so that the posterior aboral edge of the unit is blade-like. 
The anterior aboral edge of the blade is also thin. 

Cavusgnathus unicornis Youngquist & Miller 
Plate 31, figs. 13a, b 

1949 Cavusgnathus unicornis Youngquist & Miller : 619, PI. 101, figs. 18-23. 

1947 Cavusgnathus cristata Cooper (partim) : 91, PI. 20, figs. 7-10 only. 

1957 Cavusgnathus unicornis Youngquist & Miller ; Rexroad : 17, PI. 1, fig. 7. 

1957 ' Cavusgnathus unicornis Youngquist & Miller ; Lys & Serre : 1042, PI. 2, figs. 3a, b. 

1958 Cavusgnathus unicornis Youngquist & Miller ; Rexroad : 17, PI. 1, figs. 6-11. 

1961 Cavusgnathus unicornis Youngquist & Miller ; Rexroad & Burton : 1152, PI. 138, 

figs. 10-12. 
1961 Cavusgnathus unicornis Youngquist & Miller ; Rexroad & Collinson : PI. 1. 

1963 Cavusgnathus unicornis Youngquist & Miller ; Rexroad & Collinson : 9, PI. 1, figs. 
26-27. 

1964 Cavusgnathus unicornis Youngquist & Miller ; Rexroad & Furnish : 670, PI. 111, fig. 6. 

1965 Cavusgnathus unicornis Youngquist & Miller ; Rexroad & Nicoll : 18, PI. 1, figs. 18-20. 

Material. 131 specimens : figured, X 329. 

Range. North Crop CYD 6-3D 14/15, Avon Gorge C 34-D 26. 

Description. The most distinctive feature of this species is the conspicuously 
large posterior denticle of the anterior blade. 

In aboral view the cavity is a conspicuous feature of the unit. It tends to be 



BRITISH AVONIAN CONODONT FAUNAS 83 

asymmetrical in detail, the inner side being rather wider than the outer, and some- 
times starting a little anteriorly to the outer. The widest part of the cavity occurs 
in the anterior third. It is extended posteriorly as a narrow, elongate pointed cavity. 
It is deepest in its anterior half. 

In oral view the unit tapers regularly towards the posterior end, the narrowing 
being especially conspicuous in the posterior fifth. It is widest near the position of 
the largest denticle on the anterior blade and its sides are more or less straight, 
though in a few specimens they may be gently convex. The inner and outer 
parapets are ornamented by a number of transverse, parallel, straight ridges, which 
tend to be node-like in younger forms. They are most strongly developed in the 
anterior half and are relatively short, not reaching the broad, shallow, concave 
trough, which extends along the median part of the platform. There is a tendency 
for a slight central carina with two or three nodes to develop in the posterior one- 
fifth or one-sixth of the unit. There is a very conspicuous median depression on the 
inner side of the anterior blade and the inner anterior margin of the platform is 
strongly deflected inwards. In lateral view the oral and aboral edges are gently 
convex and the outer parapet is very slightly higher than the inner. 

The anterior blade slopes sharply downward from the largest denticle on the 
posterior end. Its anterior aboral margin is bluntly spatulate and it bears a series of 
inconspicuous node-like serrations along its length. These tend to gradually 
increase in size towards the posterior end, the posterior denticle being enormously 
expanded. It is not very high, but it is greatly elongated anterio-posteriorly, so 
that it resembles a shark fin, with a convex anterior edge and a straight or concave 
posterior edge. It is bluntly pointed, with more or less flat lateral faces and blunt 
anterior and posterior edges. The overall profile of the anterior blade may be gently 
convex or straight. It is about one-third the total length of the unit, but only about 
half of it is actually free of the platform. The anterior and posterior edges of the 
unit are almost vertical. 

Remarks. Rexroad (1958) remarked on the changes which occurred during 
ontogeny. Similar ontogenetic changes have been noted in the present study. The 
young specimens tend to be narrow, with parapets which are nearly straight. In 
more mature specimens the platform broadens without a corresponding increase in 
length and the flare of the inner lip of the basal cavity also increases. The number of 
small denticles on the anterior blade, anterior to the prominent posterior denticle, 
also increases. A feature of the juveniles, which Rexroad did not note, was their 
tendency to develop a row of nodes on the parapet, rather than ridges. 

Cavusgnathus unicornis resembles C. char actus and C. convexus in the convex out- 
fine of the platform in lateral view. However C. unicornis is distinctive because of 
the high posterior denticle of the anterior blade. 

There is a tendency in some specimens for the outer lateral face to be offset near 
the position of the largest denticle. The carina in the posterior portion of the 
platform seems to occur only in the largest individuals. 

Young individuals of this species from the present faunas agree with Rexroad's 
description (1958 : 17). Older individuals in our D collections have been identified 



84 BRITISH AVONIAN CONODONT FAUNAS 

by Dr. Rexroad as C. naviculus. We suspect that C. unicornis may be synonymous 
with C. naviculus. 

Cavusgnathus ? sp. nov. A 
Plate 9, figs, ioa-d 

Material. 2 specimens : figured, X 70. 
Locality and horizon. North Crop, ZLA 32. 
Range. North Crop ZLA 32. 

Description. A cavusgnathid with the anterior blade developed on the left side 
when viewed from the posterior. 

The unit is highly reminiscent of species referable to the genus Cavusgnathus but 
the free blade is developed on the opposite side, that is, the left side, when viewed 
from the posterior. The platform is long, sinuous and deep, being ornamented by 
transverse ridges which become obsolescent towards the deep median trough. The 
trough is sinuous, deep, deepening towards the anterior, with a suggestion of a carina 
filling it near the posterior termination. The blade is broken, but can be seen to be 
situated on the opposite side of the platform to known cavusgnathids ; it appears to 
be high and formed of laterally compressed denticles. 

In aboral view the basal cavity occupies the whole platform area, the lips being 
flared, especially on the blade side, and on the posterior part of the non-bladed side. 

Remarks. All known species of Cavusgnathus are asymmetrical units, the lateral 
blade being found on one side only and no mirror images being known (Rexroad 
in Lindstrom 1964 : 124). The above form is, in fact, a mirror image of a typical 
individual of the genus Cavusgnathus. 

Genus CLYDAGNATHUS gen. nov. 

Derivation of name. From the River Clydach. 

Diagnosis. A lanceolate, curved platform unit, with short anterior blade, an 
elongate platform and medial trough. The blade is medial to lateral ; the platform 
is ornamented and may bear a posteriorly restricted carina ; basal cavity asym- 
metrical. The phylogenetic origin and stratigraphic range are described below 
(P- 85). 

Type species. Clydagnathus cavusformis gen. et. sp. nov. 

Description. The blade is medial to lateral, short, and slopes anteriorly. The 
platform is lanceolate, elongated, bowed and laterally curved. It bears variable 
marginal ornament, ranging from nodes to transverse ridges. A medial trough is 
present, except at the posterior end, where a short medial carina is sometimes present 
which occasionally extends beyond the platform as a posterior blade. The asymmet- 
rical cavity is expanded, but is medially situated beneath the platform. The unit 
is not grooved. 

Remarks. This genus is closely allied to Scaphignathus and Cavusgnathus. 



BRITISH AVONIAN CONODONT FAUNAS 



85 



Many adult specimens of Scaphignathus (illustrated by Helms 1959) have a similar 
appearance to juveniles of Clydagnathus. The present genus can be distinguished 
by the lack of a carina on the oral surface of the platform (except at the posterior 
extremity) and the distinct basal cavity. Clydagnathus can be distinguished from 
Cavusgnathus by the general anterior closure of the oral trough, by the merging of the 
marginal ornament with the blade, and by the lateral, rather than longitudinal, 
expansion of the cavity. It is thought that Clydagnathus was derived from Spatho- 
gnathodus plumulus plumulus by addition of nodes and lateral movement of the 
blade. Scaphignathus probably arose from a polygnathid ancestor and Cavusg- 
nathus was derived from Taphrognathus (Rexroad and Collinson 1963). Thus none 
of the three broadly homoeomorphic genera Scaphignathus, Clydagnathus and Cavusg- 
nathus is related genetically and their different positions in the stratigraphical 
column justify the use of distinct generic nomenclature. The use of distinct generic 
names is a reflection of their distinct phylogenetic origin as well as an aid to strati- 
graphy, although the degree of morphological difference between them is less than 
that between most other platform genera. 

Clydagnathus cavusformis sp. nov. 
Plate 1, figs. 9~i3d 

Derivation of name. From the close resemblance to the genus Cavusgnathus. 

Diagnosis. Clydagnathid with lateral anterior blade very short, plume-like and 
sub-triangular in lateral profile, consisting of about four to six fused denticles with 
free, bluntly chevron shaped tips, largest near the posterior end. 



Anterior 




Posteri or 



Anterior aboral tip 



Inner latera I view 



Outer side 




Carina 



Medial trough 




Basal covity 



Orol view 



Aboral view 



Fig. 20. Clydagnathus sp. showing morphological terms used in the text. 



86 BRITISH AVONIAN CONODONT FAUNAS 

Material. 20 specimens : Holotype X 75, Paratypes X 71, x 7 2 > X 73, X 74 
(all figured). 

Type locality and horizon. R. Clydach, Nr. Gilwern, K Zone. North Crop. 
Sample KL 5. 

Range. North Crop KL i-KL 12, Avon Gorge K 12-K 17. 

Description. The blade is short, being only a quarter to a fifth the length of the 
platform. It is lateral in position, sub-triangular in profile and bears 4 to 9 fused, 
erect denticles with distinct apices. The largest denticle of the anterior blade is near 
the posterior end. The anterior aboral tip is bluntly spatulate. The platform is 
long and rather pointed, bearing lateral nodes separated by a medial trough, which 
usually deepens anteriorly (e.g. PI. 1, fig. 11). In adult specimens the lateral ridges 
may coalesce medially, to form a sharply sinuous longitudinal ridge in the posterior 
portion, the medial trough then being confined to the anteriormost portion of the 
platform (e.g. X 72, PI. 1, fig. 9). In other specimens the lateral ridges may be con- 
tinuous across the platform dividing it into a series of isolated laterally elongated 
troughs (e.g. X 73, PI. 1, fig. 10), with a more or less prominent longitudinal marginal 
ridge on one side. The platform may be very slender, elongate and sinuous (e.g. 
X 74, X 75, PI. 1, figs. 13, 11). The posterior part may bear a short restricted carina 
of rounded, isolated nodes (e.g. X 75, PI. 1, fig. 11) which can be produced as a short 
posterior blade. The inner oral rim of the platform is deflected through 80 °, at the 
anterior end, so preventing the trough from opening anteriorly. 

The cavity is large, asymmetrical with thickened lips and is conspicuously laterally 
expanded. 

Remarks. This species is closely related to C. gilwernensis, from which it differs 
by having a lateral blade rather than a medial one. It can be distinguished from the 
genus Cavusgnathus by the closed medial trough and the pseudopolygnathid type of 
asymmetrical sub-circular basal cavity. 

Clydagnathus darensis sp. nov. 
Plate 2, fig. 6a-7d 

Derivation of name. From the type locality at Daren Ddu. 

Diagnosis. Clydagnathid with relatively low, short anterior blade, consisting of 
4 or 5 more or less erect denticles, those at the anterior end being only slightly 
smaller than those at the posterior. 

Material. 23 specimens : Holotype X 77, Paratype X 76 (both figured). 

Type locality and horizon. R. Clydach, Nr. Gilwern, Lower Z Zone. Sample 
ZLA 27. 

Range. North Crop ZL 3-ZLA 27, Avon Gorge K 17. 

Description. The unit is asymmetrical, the blade always being on the right 
when viewed from the posterior. The blade is low, consisting of 4 or 5 denticles all 
of approximately equal height, the tallest denticle being either the posterior or the 



BRITISH AVONIAN CONODONT FAUNAS 87 

penultimate posterior. The platform is ornamented by two rows of irregular nodes. 
The margins are separated by a shallow trough, which generally tends to close 
towards the anterior, and occasionally possess a short carina at the posterior 
extremity. The lateral denticles on the blade side of the platform tend to be rather 
larger than those on the other side. In smaller specimens, the basally confluent 
platform denticles have sharply pointed, discrete apices in lateral view, but they 
become more blunt in larger specimens. The platform walls are deep, and the aboral 
outline is straight over the anterior two-thirds, but the posterior one-third can be 
deflected downwards, especially in smaller specimens. 

In aboral view, the unit is excavated, the cavity being large, flaring and asym- 
metrical, extending from nearly the posterior extremity of the platform to its 
junction with the anterior blade. 

Remarks. This species can be distinguished from all other clydagnathids by 
the character of the blade. 

Clydagnathus gilwernensis sp. nov. 
Plate 2, fig. ia-d 

Derivation of name. From the locality at Gilwern. 

Diagnosis. Clydagnathid with short, high, medial, anterior blade, and short 
posterior carina occasionally developed into a short posterior blade. 

Material. 7 specimens : Holotype X 78 (figured). 

Type locality and horizon. R. Clydach, Nr. Gilwern, K Zone. North Crop. 
Sample KL 1. 

Range. North Crop KL i-KL 6, Avon Gorge K 6. 

Description. The anterior blade is short and situated medially. It commonly 
bears three denticles, the posteriormost being the tallest and most massive. The 
blade denticles, which have blunt or chevron tips, are laterally compressed, and are 
fused at their bases. They decrease rapidly in size anteriorly. The anterio-aboral 
portion of the blade is strongly protruding and bluntly spatulate in profile. The 
platform is long, slender and posteriorly sharply pointed ; it has two lateral rows of 
blunt, triangular lateral nodes, with a shallow medial trough which is filled at the 
posteriormost extremity by a short carina of 2 to 4 nodes, which may extend beyond 
the platform to give a short posterior blade. On some specimens the carina may be 
absent. 

In lateral view the posterior platform of young forms is " upstepped " relative to 
the blade, but in mature specimens the unit is arched about the cavity. 

In aboral view there is an asymmetrical medial cavity situated in the anterior 
third of the platform. It has longitudinally thickened lips ; a faint groove some- 
times runs a short distance either side of the cavity. 

Remarks. In gross morphological terms C. gilwernensis is similar to Patrognathus 
variabilis but the vastly different cavity, the distinctive blade and excavated medial 
trough serve to distinguish it. It would appear that the two forms were the result 



88 BRITISH AVONIAN CONODONT FAUNAS 

of convergent evolution, since the ancestors of C. gilwernensis were of spathogna- 
thodid stock. They may have been functionally similar. 

Clydagnathus unicornis sp. nov. 
Plate 2, figs. 2a~3d, 5a, b 

Derivation of name. From the single large denticle on the blade. 

Diagnosis. Clydagnathid with restricted anterior lateral blade, consisting 
essentially of one large denticle ; median trough opens anteriorly ; basal cavity 
elongated and symmetrical. 

Material. 25 specimens : Holotype X 79, Paratypes X 80, X 81 (all figured). 

Type locality and horizon. R. Clydach, Nr. Gilwern, Lower Z Zone. North 
Crop. Sample Z 2A. 

Range. North Crop ZL 4-ZLA 27, Avon Gorge Z 1. 

Description. The unit is asymmetrical, the blade always occurring on the right 
side viewed from the posterior, and consisting essentially of one large denticle, sub- 
triangular in shape and posteriorly inclined. The tip of the denticle is sharply 
pointed and the anterior edge convex, forming a continuous curve with the spatulate 
antero-aboral margin of the blade. The anterior face of this denticle occasionally 
bears 2 or 3 small denticles which are fused with it, so that only thin blunt apices 
are visible. 

The platform is uneven, consisting of two rows of low irregular marginal nodes, 
separated by a very shallow, but rather wide, medial trough. A short carina may 
sometimes be present in the posterior extremity. The platform walls are deep, and 
on the basal faces are disrupted by the flaring of the lips of the basal cavity. In 
lateral view, the marginal nodes are sharply pointed in smaller specimens, but blunt 
or flat in larger specimens. 

In aboral view the unit is excavated, the cavity being asymmetrical, expanded 
more on the inner side than the outer. The cavity runs posteriorly, becoming 
narrower and shallower towards the posterior termination. It is grooved along its 
whole length. 

Remarks. This species probably arose from Clydagnathus cavusformis by fusion 
of the anteriormost blade denticles to give an essentially unidenticulate blade, and 
by the elongation of the cavity, rather than the laterally expanded cavity of C. 
cavusformis. 

Clydagnathus sp. nov. A 
Plate 2, figs. 4a-d 

Material. 2 specimens : figured, X 82. 
Range. North Crop KL 7-KL 13. 



BRITISH AVONIAN CONODONT FAUNAS 



89 



Description. A clydagnathid with a high, equally tridenticulate anterior blade, 
a short posterior blade, and a heavy asymmetrical basal cavity. 

The unit is arched and triangular in cross-section. The blade is short and high, 
consisting of three equal denticles fused into a blade but with free tips which are 
slightly divergent. The platform is lanceolate, nearly four times as long as wide, 
and is ornamented with two rows of denticles along the platform margins, separated 
by a straight, shallow, smooth trough. The denticles tend to be transversely 
elongate. The posterior part of the platform possesses a short carina, of about three 
nodes, which is produced posteriorly to give a short posterior blade. 

In lateral view the platform posterior to the basal cavity is deflected continuously 
downwards through 30 °, and its depth decreases markedly towards the posterior. 
The basal cavity is large, ovate, nearly symmetrical and is confined to the anterior 
part of the platform ; it flares slightly in lateral view. 

Remarks. This clydagnathid is similar to C. darensis, but the blade is much 
higher, has fewer denticles and the deflected posterior platform is unique. The 
cavity is also different in that all other clydagnathids have an obviously asymmetrical 
cavity, whereas this form possesses a nearly symmetrical cavity. 



Genus EUPRIONIODINA Ulrich & Bassler 1926 



1925 Euprioniodina Bassler : 219. (nom. nud.) 

1925 Synprioniodina Bassler : 219. (nom. nud.) 

1926 Eupvio::'. ' .-; Ulrich & Bassler : 29. 
1926 Synprioniodina Ulrich & Bassler : 42. 



Type species. Eupvioniodina deflecta Ulrich and Bassler 1926. 

Description. This genus is characterized by its general pick-shape, with a short, 



denticulated, highly compressed anticusp. 
numerous erect denticles. 



The posterior limb is long and bears 



Apical denticle 



$. ^^.Dentlcles 



Anterior bar 




Posterior bar 



Outer lateral face 



Aborol margin 



Fig. 21. Eupvioniodina sp. showing morphological terms used in the text. 



go BRITISH AVONIAN CONODONT FAUNAS 

Remarks. The genera Synprioniodina, Euprioniodina and Neoprioniodus have 
essentially the same outline and differ in the presence, or absence, of denticles on the 
anticusp. The genera Synprioniodina and Euprioniodina are here considered 
synonyms and are characterized by a denticulated anticusp. Neoprioniodus is a 
similar pick-shaped form to Euprioniodina, but has no denticulated anticusp. 

As Scott and Collinson (1961) pointed out, there appears to be a number of forms 
intermediate between Euprioniodina and Neoprioniodus. Sannemann (1955) » 
Bischoff (1956) and Helms (1959) have assigned all such specimens to the genus 
Prioniodina. However, the specimens they refer to Prioniodina do not closely 
resemble the type species of Prioniodina, Prioniodina subcurvata. A detailed 
revision of the pick-shaped forms is necessary, but as few specimens referable to the 
genus Euprioniodina have been found in the present faunas, it is impossible to under- 
take this study. 

It is difficult to distinguish Euprioniodina from some species of Apatognathus. 
We have divided the two genera by assigning to Apatognathus those species in which 
there is conspicuous lateral flexing of one or both bars. 

Euprioniodina caverna (Collinson & Druce) 
Plate 22, figs. 11a, b 

Synprioniodina caverna Collinson & Druce in press. 

Material. 14 specimens : figured, X 83. 

Range. North Crop 3D 14/15. 

Description. The present specimens have a greatly elongated anterior bar, 
which is more or less straight, and which bears a series of at least twelve laterally 
compressed, confluent denticles on its anterior edge. These are small and of uniform 
size, being considerably smaller than any of those on the posterior bar. The apical 
denticle, which is aligned with the main line of the anterior bar, is relatively short ; 
it is sharply pointed, with sharp anterior edges and a gently convex outer lateral face. 
The junction of the anterior and posterior bars is marked by the development of an 
apical lamella, which is depressed and has a flat surface in outer lateral view. The 
posterior bar is straight to feebly convex in outer lateral view and is also flexed 
inwardly. It bears a series of about 14 denticles on its oral edge, which show a broad 
tendency to increase in size posteriorly, though this is not a regular feature. They 
are basally confluent but apically discrete and are elongated and pointed, being at 
least two to three times as long as those of the anterior bar. They are directed 
forward parallel to the apicle denticle and are also curved gently inward. 

In inner lateral view the surface of the posterior bar is gently convex, and that of 
the anterior bar more or less flat. The denticles are distinctly curved inward and 
there is a very sharp aboral flexure below the apical denticle with an angular to 
strongly convex apical lamella. 

The aboral surface is excavated by a narrow groove along the whole of its length, 
this being a continuation of the wide flaring cavity below the apical lamella. 



BRITISH AVONIAN CONODONT FAUNAS 91 

Euprioniodina microdenta (Ellison) 
Plate 22, figs. 16a, b 

*933 Synprioniodina sp. Gunnell : 269, PI. 31, fig. 6. 

1941 Synprioniodina microdenta Ellison : 108-111, 119, PI. 20, figs. 43-46. 

1941 Synprioniodina microdenta Ellison ; Ellison & Graves : 3-4, PI. 1, fig. 10. 

1944 Synprioniodina microdenta Ellison ; Branson : 327. 

1952 Synprioniodina microdenta Ellison ; Rhodes : 893, PI. 126, fig. 4. 

Material. 2 specimens : figured, X 84. 

Range. North Crop 3D 4-3D 14/15. 

Description. The present specimens are characterized by a very short anterior 
bar and a greatly elongated posterior bar. In outer lateral view the posterior bar is 
greatly elongated, tending to increase in depth posteriorly. Its outer lateral face is 
flat to gently convex, and it is about equal in depth to the length of the free denticles. 
Its oral surface bears about 14 long, slender denticles, more or less subcircular in 
cross-section, though showing a slight tendency to lateral flattening. They are 
discrete for most of their length and are sharply pointed. They are separated by 
very much finer needle-like denticles, which are only a quarter to a third the width of 
those of the major series. All denticles slope anteriorly, and are also more or less 
curved inwards. They tend to increase in size towards the posterior third of the bar. 
The outer lateral face of the main cusp is gently convex and it has conspicuously 
sharp anterior and posterior edges. The anterior bar is very short, being only about 
one-sixth the length of the posterior ; it tapers rapidly towards its distal end. It 
bears 3 or 4 minute denticles, which lie parallel to the main cusp. In inner view the 
whole unit is gently flexed, so that the inner lateral faces are very feebly concave. 
The aboral margin of the posterior bar is more or less straight in lateral view, apart 
from its rapid curvature below the apical denticle. The two bars diverge at an angle 
of about 60 °. The apical denticle is about three times the width of the largest 
denticles of the posterior bar. 

Euprioniodina sp. nov. A 
Plate 22, figs. 13a, b 

Material, i specimen : Holotype X 86 (figured). 

Locality and horizon. Hosie Limestone, Fife Coalfield. Sample HOSIE 2B. 

Range. Scotland HOSIE 2B. 

Description. A Euprioniodina with a massive, laterally compressed, incurved and 
recurved apical denticle. The anterior bar is short and pointed with up to three 
confluent denticles. The posterior bar is short with three minute denticles developed 
on the posterior edge of the apical denticle. 

The present specimen is very fragmentary, but it shows a massive apical denticle 
which is laterally compressed with sharp anterior edges and gently convex lateral 
faces. It is recurved sharply posteriorly in its lower portion. The short anterior 
bar is pointed and bears a series of two or three confluent denticles on its oral edge 



92 BRITISH AVONIAN CONODONT FAUNAS 

which tend to decrease in size anteriorly. Three very small, confluent, laterally 
compressed denticles are developed on the posterior edge of the apical denticle. 
These are of minute size. The anterior aboral lateral face of the apical denticle is 
very strongly expanded laterally, whereas that of the outer lateral face is flat to 
feebly convex. The posterior bar is shallow and strongly laterally compressed, its 
outer lateral face being flat and its inner very feebly convex. The apical denticle is 
incurved as well as recurved. 

Euprioniodina sp. 
Plate 22, figs. 15a, b 

Material. 16 specimens : figured, X 85. 

Range. Avon Gorge K 4-K2 I. 

Description. The apical denticle is relatively short and compressed, with a 
denticulate anticusp equal in length to the apical denticle. The apical denticle is 
strongly compressed laterally, with sharp anterior and posterior edges. The anticusp 
is a continuation of the main denticle and both are slightly concave inward. The 
anticusp bears up to 5 laterally compressed denticles, the anterior margins of which 
are subparallel to the apical denticle. The posterior limb is long and thin, and is 
sharply bowed immediately posterior to the apical denticle, with little additional 
bowing behind this. The entire unit is sharply arched. The posterior limb is 
straight and bears at least 14 confluent, sub-equal, sub-rounded to laterally com- 
pressed denticles. The minute pit is located at the base of the cusp and has slightly 
flared lateral lips. The pit is deep, with a sharp point extending into the base of the 
apical denticle. 

Genus GENICULATUS Hass 1953 

x 953 Geniculatus Hass : 77. 

Type species. Polygnathus ? claviger Roundy 1926. 

Geniculatus sp. 
Plate 31, fig. 24 

Material. 2 specimens : figured X 327. 

Range. Scotland DUN 59. 

Description. Two broken specimens are present in one sample from Dunbar. 
Both specimens are anterior bars which are greatly inflated and bear a series of 
laterally compressed fused denticles with free chevron tips. In aboral view the bar 
is broad and has a fine median groove. 

Remarks. The inflated bar enables the present specimens, although broken, to 
be referred to Geniculatus. 



BRITISH AVONIAN CONODONT FAUNAS 



93 



Genus GNATHODUS Pander 1856 
1856 Gnathodus Pander : 33. 

Type species. Gnathodus mosquensis Pander 1856. 

Gnathodus antetexanus Rexroad & Scott 
Plate 18, figs. 6a-c, 8a, b, I3a-d 

1947 Gnathodus texanus Roundy ; Mehl & Thomas : 10, PI. i, fig. 3. 

x 957 Gnathodus texanus Roundy ; Bischoff (partim) : 25, PI. 3, fig. 22 only. 

J 959 Gnathodus texanus Roundy ; Voges {partim) : 284, PI. 33, figs. 40, 42 only. 

1962 Gnathodus n. sp. aff. Gnathodus texanus Roundy; Collinson, Scott & Rexroad : chart 3. 

1964 Gnathodus antetexanus Rexroad & Scott : 28, PI. 2, figs. 7-10. 

Material. 10 specimens : figured, X 412, X 413, X 414. 

Range. North Crop ZLA 32-ZLA 33, Avon Gorge Z 33-C 9. 

Description. Most of our specimens are broken, but the platforms are preserved. 
They show the typical narrow outer platform, with a sparse covering of nodes, and 
the broader inner platform with the large upstanding node, which are characteristic 

Posterior Posterior 



Outer side of 

plotform 



Node 




Inner side of 

platform 



Carino 



Blade 




Basal cavity 



Anterior 
A. Oral view 



Anterior 
B. A bora I view 



Denticles of blade 




Nodes of platform 
Carino 

Platform 



Blade 



C Lot 



eral view 



Fig. 22. Gnathodus sp. showing morphological terms used in the text. 



94 BRITISH AVONIAN CONODONT FAUNAS 

features of the species. They are very similar to the specimens illustrated by 
Rexroad and Scott. 

Gnathodus avonensis sp. nov. 
Plate 18, figs. o,a-d 

Derivation of name. After the type section in the Avon Gorge. 

Diagnosis. Gnathodus avonensis sp. nov. is closely similar to Gnathodus simplicatus 
sp. nov. but bears a node on one side of upper surface of platform. 

Material. 2 specimens : Holotype X 411 (figured). 

Type locality and horizon. Avon Gorge Z2 Limestone. Sample Z 38. 

Range. Avon Gorge Z 38. 

Description. The platform is confined to the posterior third of the unit and is 
unornamented except for the presence of a single node on one side of the platform. 
It is biconvex in outline and narrow. In lateral view the blade is rather rectangular 
in outline, the 10 or more denticles being of uniform size. The anterior edge is 
straight, and forms a right angle with the aboral edge of the blade, which may be 
slightly curved. The oral edge is straight in the anterior half of the unit and slightly 
arched in the posterior half of the unit. The platform has a concave aboral margin 
in lateral view, and is less deep than the blade. There is a flaring and elongate 
basal cavity below the platform. 

Remarks. Gnathodus avonensis sp. nov. developed from G. simplicatus sp. nov. 
by the formation of a single node on the side of the platform. G. avonensis sp. nov. 
is a homoeomorph of G. nodosus Bischoff. 

Gnathodus bilineatus (Roundy) 
Plate 18, figs. I4a-I7d 

1900 Polygnathus [Gnathodus) Mosquensis Pander (sic) Hinde : 342, PI. 9, figs. 2-4. 

1926 Polygnathus bilineatus Roundy : 13, PI. 3, figs, ioa-c. 

1926 Polygnathus texanus Roundy : 14, PI. 3, figs. 13a, b. 

1928 Gnathodus mosquensis (Pander) Holmes : 6, fig. 31. 

1939 non Gnathodus bilineatus Cooper : 388, PI. 42, figs. 59-60. 

1941 Gnathodus pustulosus Branson & Mehl : 172, PI. 5, figs. 32-39. 

1953 Gnathodus bilineatus (Roundy) Hass : 78, PI. 14, figs. 25-29. 

1956 Gnathodus bilineatus (Roundy) Elias : 118, PI. 3, figs. 23-29. 

1956 Gnathodus pustulosus (Branson & Mehl) Elias : 115, PI. 3, figs. 1-8. 

1957 Gnathodus bilineatus bilineatus (Roundy) Bischoff : 21, PI. 3, figs. 11, 15-20 ; 

PI. 4. %• I- 
1957 Gnathodus bilineatus bilineatus (Roundy) Ziegler in Flugel & Ziegler : 38, PI. 3, figs. 
1, 2 only. 

1957 Gnathodus modocensis Rexroad : 30, 31, PI. 1, figs. 15-17. 

1958 Gnathodus modocensis Rexroad ; Rexroad : 17, 18, PI. 1, figs. 1, 2. 

1959 Gnathodus bilineatus (Roundy) Voges : 282, PI. 33, figs. 28-30. 

1959 Gnathodus (Harltonodus) bilineatus (Roundy) Elias : 145, PI. 1, figs. 3-12. 

1959 Gnathodus (Harltonodus) bransoni Elias : 147, PI. 1, figs. 13-18. 

1959 Gnathodus (Harltonodus) minutus Elias : 148, PI. 1, figs. 22-25. 

1959 Gnathodus (Harltonodus) multilineatus Elias : 149, PI. 1, figs. 26-28. 



BRITISH AVONIAN CONODONT FAUNAS 95 

i960 Gnathodus smithi Clarke : 26, PI. 4, figs. 13-14 ; PI. 5, figs. 9 & 10. 

1961 Gnathodus bilineatus (Roundy) Higgins : PI. 10, fig. 5. 

1962 Gnathodus bilineatus (Roundy) Higgins : (partim), PI. 2, fig. 25 only. 
1962 Gnathodus bilineatus bilineatus (Roundy) Meischner : 31, fig. 10. 
1965 Gnathodus bilineatus (Roundy) Dunn : 1148, PI. 140, figs. 7-9. 

Gnathodus bilineatus (Roundy) Collinson & Druce in press. 

Material. 765 specimens, North Crop : figured X 416, X 417, X 93, X 94. 

Range. North Crop 3D 10-3D 23. 

Description. This is one of the most abundant species in the higher parts of the 
section of the North Crop and, although it displays considerable variation, its main 
features agree closely with those described by earlier authors, especially Hass (1953) 
and Bischoff (1957). There is considerable variation in the ontogeny of this 
species. The main variation concerns the increase in the relative size and angularity 
of outline of the outer lateral platform, and its increasingly strongly developed 
ornamentation. In young forms this tends to be inconspicuously nodose and 
rather irregular, but in older forms it becomes either longitudinally linear or 
broadly concentric in disposition, and the nodes become stronger, tending to form 
elongate ridges. There is also considerable variation in the strength of the inner 
lateral platform and of the transverse denticles developed upon it. In numbers of 
specimens it is pinched inwards in the anterior half when seen in oral view. There is 
also appreciable variation in the depth and relative width of the sulcus that separates 
these denticles from the carina. In spite of its extent, the variation appears to be 
continuous, and there is no obvious difference between specimens collected from 
different parts of the range of the species. 



Gnathodus commutatus (Branson & Mehl) 
Plate 19, figs. ga-i2d 

1941 Spathognatkodus commutatus Branson & Mehl : 98, PI. 19, figs. 1-4. 

1941 Spathognatkodus commutatus Branson & Mehl ; Ellison & Graves : 3, 4. PI. 2, 

fig. 6, (non PI. 2, fig. 4 = Gnathodus symmutatusl) . 
1953 Gnathodus inornatus Hass : 80, PI. 14, figs. 9-1 1. 

1956 Spathognatkodus commutatus Branson & Mehl ; Elias : 119, PI. 3, figs. 19-22. 
1956 Spathognatkodus inornatus Hass ; Elias : 119, PI. 3, figs. 37-39. 

1956 Spathognatkodus cf. inornatus Elias : 119, PI. 3, figs. 41, 42, (non PI. 3, figs. 62, 63 = G. 
symmutatus?) . 

1957 Gnathodus commutatus commutatus (Branson & Mehl) Bischoff : 22, PI. 4, figs. 2-6, 

15- 
J 957 Spathognatkodus cf. S. commutatus Branson & Mehl ; Rexroad : 38, PI. 3, figs. 23, 24. 
? 1957 Gnathodus commutatus commutatus (Branson & Mehl) Ziegler in Flugel & Ziegler 
39, PI. 3, fig. 21. 

1958 Gnathodus inornatus Hass ; Stanley : 465, PI. 68, figs. 5, 6. 

1958 Spathognatkodus cf. S. commutatus Branson & Mehl ; Rexroad : 26, PI. 6, fig. 8. 



96 BRITISH AVONIAN CONODONT FAUNAS 

non 1958 Gnathodus commutatus commutatus (Branson & Mehl) Lys & Serre : 891, PI. 9, 
figs. 2a, b (-G. symmntatus) . 

1959 Gnathodus commutatus commutatus (Branson & Mehl) Voges : 281. 

1960 Spathognathodus commutatus Branson & Mehl ; Clarke : 19, PI. 3, figs. 4, 5. 
i960 Gnathodus commutatus commutatus (Branson & Mehl) Serre & Lys : 39, fig. 3. 

1961 Gnathodus commutatus (Branson & Mehl) Rexroad & Burton : 1153, PI. 139, figs. 

i-3- 

1961 Gnathodus commutatus var. commutatus (Branson & Mehl) Higgins : 212, PI. io, 
figs. 6, text-fig. ia, (left figure only). 

1962 Gnathodus commutatus commutatus (Branson & Mehl) Higgins : PI. 2, fig. 22. 

1962 Gnathodus commutatus commutatus (Branson & Mehl) Meischncr : 31, text-fig. 10. 

1963 Gnathodus commutatus commutatus (Branson & Mehl) Bouckaert & Higgins : 17, 

ng- 3 

1964 Gnathodus commutatus pellaensis Rexroad & Furnish : 671, PI. in, fig. 3. 
Gnathodus commutatus (Branson & Mehl) Collinson & Druce in press. 

Material. 425 specimens : figured, X 418, X 95, X 96, X 97. 

Range. North Crop CYD 7-3D 22, Avon Gorge S 53. 

Description. This species has recently been redefined by Collinson & Druce 
(in press) and it is their revised description which is accepted here. Although the 
species, which is represented by many specimens in the present collections, shows 
appreciable variation, the distinctive characteristics are the regular sub-rectangular 
outline of the blade when seen in lateral view, the regular height and thickness of the 
confluent denticles which make up the blade, the rather square anterior profile of the 
blade, and the small posteriorly restricted sub-oval to sub-circular unornamented 
platform. This platform is always asymmetrical in detail, and shows considerable 
variation in its basal outline and in the degree of flexure of its basal margin. This 
variation is so obviously transitional, however, that it seems impossible to dis- 
tinguish any discrete categories on the basis of it. The chief variation is in the 
general form of the posterior platform, which varies from slenderly sub-elliptical to 
sub-circular, in the degree of symmetry of the posterior platform, which is generally 
marked by the inner margin being wider anteriorly than it is posteriorly, and in the 
relation of the carina to the posterior margin of the platform. In some cases the 
posterior margin of the platform tends to be relatively elongated, while in others it 
tends to be bluntly rounded. The carina may, in some specimens, extend slightly 
beyond the posterior margin when seen in oral view (PI. 19, fig. 9d) but in others it 
terminates anteriorly to the margin. In a few cases the posterior portion of the 
carina is strongly deflected laterally. In most individuals the central blade tends to 
become thicker posteriorly, where it forms the carina of the posterior platform (e.g. 
PI. 19, fig. iod). The surface of the posterior platform is smooth and the platform 
itself occupies only the posterior quarter or third of the total length of the unit. 
The broad variation within this species noted by Collinson and Druce is also shown 
by the present specimens. 

Remarks. In many specimens the blade is straight, but in others it is gently 
curved in a horizontal plane ; in these cases the wider of the two platforms in the 
anterior position is always that on the concave side of the blade. 



BRITISH AVONIAN CONODONT FAUNAS 97 

Gnathodus cuneiformis Mehl & Thomas 
Plate 8, figs. 6a-c 

1939 Gnathodus mosquensis Pander ; Cooper (partim) : 388, PI. 41, figs. 23-25 only ; PI. 42, 

figs. 75, 76. 
*939 Gnathodus stinus Cooper : 388, PL 14, figs. 40, 41. 
1947 Gnathodus cuneiformis Mehl & Thomas : 10, PI. 1, fig. 2. 
1962 Gnathodus cuneiformis Mehl & Thomas ; Collinson Scott & Rexroad : Chart 3, p. 10, 

22, 23. 

Material, i specimen : figured, X 98. 

Range. Avon Gorge S 11. 

Description. This species is characterized by a high, slightly asymmetrical, 
arrow-shaped platform, bearing a single row of nodes on either side of the carina. 
The flanks of the platform are smooth and steep. 

Remarks. The shape of the platform and the single row of nodes on either side 
of the carina distinguish this species from other gnathodids. In North America this 
species is characteristic of the Sedalia, Fern Glen and Burlington Formations. 

Gnathodus delicatus Branson & Mehl 1938 
Plate 18, figs. I2a-d. Plate 30, figs. 6a-c 

1938 Gnathodus delicatus Branson & Mehl : 145, PL 34, figs. 25-27. 

1938 Gnathodus perplexus Branson & Mehl : 145, PL 45, fig. 24. 

J 939 Gnathodus texanus (Roundy) Cooper : 388, PL 41, figs. 26, 27. 

1951 Gnathodus delicatus Branson & Mehl ; Hass : 394, PL 46, figs. 3-7. 

1957 Gnathodus commutatus punctatus Bischoff ; Fliigel & Ziegler : PL 111, figs. 16, 17, 24. 

1959 Gnathodus delicatus Branson & Mehl ; Voges : 283, PL 33, figs. 31-33. 

i960 Gnathodus delicatus Branson & Mehl ; Kronberg, Pilger, Scherp & Ziegler : PL 4, 

figs. 7-12. 

1962 Gnathodus delicatus Branson & Mehl ; Collinson, Scott & Rexroad : 10, Chart 3, 21, 22. 

1962 Gnathodus delicatus Branson & Mehl ; Higgins : 13, PL 3, fig. 33 ; PL 2, figs. 23, 24. 

1962 Gnathodus delicatus Branson & Mehl ! Zeigler : PL 4, fig. 4. 

1963 Gnathodus delicatus Branson & Mehl ; Ziegler : 327, PL 2, figs. 5, 7, 8, 9, 13, 14. 

1963 Gnathodus delicatus cuneiformis Ziegler : PL 2, fig. 12. 

1964 Gnathodus delicatus Branson & Mehl ; Rexroad & Scott : 29-30, PL 2, figs. 4-6. 

1964 Gnathodus delicatus Branson & Mehl ; Higgins, Wagner-Gentis & Wagner : 226, PL V, 

fig. 24. 
1964 Gnathodus cf. delicatus Branson & Mehl ; Higgins, Wagner-Gentis & Wagner : 226, 

PL V, fig. 23. 

Material, ii specimens : figured, X 87, X 426. 

Range. North Crop ZLA 5-ZLA 6, Avon Gorge Z 28-Z 37. 

Description. The asymmetrical platform of this species is ornamented by two 
rows of nodes, one on the narrower inner side, and one on the wider outer side, both 
running parallel to the carina. The inner platform bears a row of up to 9 denticles 
parallel to the carina, and slopes steeply at its margin. The outer platform bears a 
row of 5 denticles, parallel to the carina, on its inner side, and may also show traces of 



98 BRITISH AVONIAN CONODONT FAUNAS 

the development of a second row. There is a uniform sharp slope towards the 
margin. The platform is arrow-shaped, being widest at the anterior. It becomes 
pointed towards the posterior. The inner platform extends further anteriorly than 
does the outer. The denticulate blade is equal in length to the platform. In lateral 
view, the oral and aboral edges of the blade are straight ; the oral and aboral edges 
of the platform are slightly curved. The anterior and posterior edges are straight. 

Remarks. Specimens from the Z2 beds of the Avon Gorge have a row of nodes on 
either side of the carina. In some examples, the anterior nodes of the inner side of 
the platform are fused to form a parapet. These forms are considered to be transi- 
tional with Gnathodus semiglaber, or possibly with Gnathodus antetexanus. 

This species is common in conodont faunas of late Kinderhookian and early 
Valmeyerian age in North America. Rexroad & Scott (1964) after studying 
hundreds of specimens, came to the conclusion that the low, broad, asymmetrical 
outline of the platform, and the linear arrangement of nodes seem to be consistent 
characters, and similar specimens obtained in the present study have, therefore, been 
placed in this species. 

Gnathodus girtyi girtyi Hass 
Plate 17, figs. ga-i2d 

1953 Gnathodus girtyi Hass : 80, PI. 14, figs. 22-24. 

1956 Gnathodus girtyi Hass ; Elias : 118, PI. 3, figs. 30, 31. 

1957 Gnathodus girtyi Hass ; Bischoff (partim) : 24-25, PI. 4, figs. 16-17, 22-23 (non PI. 4, 
fig. 21= Gnathodus girtyi simplex Dunn). 

1957 Gnathodus girtyi Hass : Lys & Serre : 1043, PI. 1, figs. 7a-c. 

1958 Gnathodus ? sp. Rexroad : 18, PL 1, figs. 3-5. 

i960 Gnathodus clavatus Clarke : 28, PI. 4, figs. 4-6 (non PI. 4, figs. j—g = G. girtyi simplex 

Dunn). 
1961 Gnathodus girtyi Hass ; Higgins : 220, PI. 10, fig. 4. 
1961 Gnathodus n. sp. Rexroad & Collinson : PI. 1. 

1961 Gnathodus girtyi Hass ; Rexroad & Jarrell : 2015. 

1962 Gnathodus girtyi Hass ; Collinson, Scott & Rexroad : Chart 4. 

1962 Gnathodus girtyi Hass Form A Meischner : 31, text-fig. 10. 

1963 Gnathodus girtyi Hass Form C Bouckaert & Higgins : 17, text-fig. 3. 
Gnathodus girtyi girtyi Hass ; Collinson & Druce in press. 

Material. 780 specimens : figured, X 103, X 104, X 105, X 106. 

Range. North Crop CYD 5-3D 23, Avon Gorge D 26. 

Description. The main features of this subspecies have been described in detail 
by Collinson & Druce (in press) and the present specimens, although showing 
some variation, agree in all major respects with their description. The most 
distinctive features are the long slender form of the unit, with the anterior blade 
commonly being strongly laterally compressed and relatively high in relation to its 
length ; it occupies at least half the total length of the unit. It is straight to curved 
in oral view. The unit as a whole is straight or curved in a horizontal plane, and the 
curvature is chiefly concentrated in the posterior portion of the carina (e.g. PI. 17, 



BRITISH AVONIAN CONODONT FAUNAS 99 

figs, ii, 12). The blade is generally highest at its anterior end, although the two 
most anterior denticles may be relatively small ; the posterior end of the unit tends 
to be lower. The blade has a bluntly spatulate to rectangular anterior end and a 
more or less straight or very feebly convex aboral edge. The denticles are fused to 
about mid-height but their apices are discrete. 

The carina consists of low, fused denticles, of about equal height to those at the 
posterior portion of the anterior blade. The carina is depressed in the posterior half 
of the platform, and the level of the denticles tends to be relatively higher than those 
of the lateral ornament, which reaches about two thirds of the total depth of the 
posterior platform from the top of the carina. The posterior platform itself is 
characterized by a variably asymmetrical basal outline. In some specimens the 
basal outline is almost biconvex, but in most the outer aboral margin is more con- 
spicuously flared than the inner ; in a few individuals it is so strongly flared that it 
gives to the basal outline a form reminiscent of such species as G. bilineatus or G. 
semiglaber (e.g. PI. 17, fig. 12a). In spite of this, the platform ornament remains 
distinctive ; the ornament on the inner lateral surface of the platform extends 
further forward than that on the outer, and consists of a low series of fused nodes, 
running sub-parallel to the carina but converging with it in the posterior platform, 
and looping round the posterior end of the carina to give a bluntly rounded, pointed 
outline (e.g. cf. PI. 17, figs. 11b, 12b). The outer platform ornament tends to be less 
conspicuous than that of the inner ; the lateral ridges, which characterize the 
denticles of the inner platform, are absent from the outer platform. 

The basal cavity is flaring and asymmetrical, being deepest in the anterior third of 
the platform and continuing for a variable distance below the posterior portion of 
the anterior blade. 

Remarks. In some individuals (e.g. PI 17, fig. 10b) the posterior carina tends to 
continue somewhat beyond the level of the lateral denticles, which then tend to merge 
with it anterior to the termination of the platform. In this they approach other 
subspecies of the genus but are otherwise distinguishable from them. 

Gnathodus girtyi collinsoni subsp. nov. 
Plate 16, figs. 5a-8d 

1962 Gnathodus girtyi Form C Meischner : 31, fig. 10. 

1963 Gnathodus girtyi B Hass ; Bouckaert & Higgins : 17. 

1965 Gnathodus roundyi Gunnell ; Murray & Chronic (partim) : 598, PI. 71, figs. 5, 6 only. 

Derivation of name. After Dr. Charles W. Collinson. 

Diagnosis. Subspecies of Gnathodus girtyi in which lateral denticulation of 
platform is confined to inner lateral side. Very feeble nodes may sometimes be 
developed on outer lateral platform. 

Material. 13 specimens : Holotype X 99, Paratypes X 100, X 101, X 102 (all 
figured) . 

Type locality and horizon. North Crop. Sample 3D 14/15. 



ioo BRITISH AVONIAN CONODONT FAUNAS 

Range. North Crop 3D 8-3D 14/15. 

Description. In broad morphology this subspecies resembles Gnathodus girtyi 
girtyi. The form of the anterior blade, and its general denticulation, the general 
outline and the size and depth of the posterior platform are generally similar. The 
number of denticles in the main blade (including the carina) ranges from 21 to 25. 

The distinctive feature of this subspecies is the denticulation of the posterior 
platform. The inner-lateral oral surface of the platform has a conspicuously 
developed, parapet-like series of denticles, those at the anterior end being higher than 
those at the posterior. These denticles are individually rather small and incon- 
spicuous, but the ridge which they form is itself made conspicuous by the general 
height and thickness of the base. They number about 9, and are small rounded 
discrete node-like structures. Those at the anterior end of the series are separated 
from the carina by a shallow longitudinal groove. Towards the posterior end of the 
series the denticles converge with the main carina, which they meet near the anterior 
end of the fourth denticle from the posterior terminus of the unit. In lateral view 
these denticles form a conspicuous shoulder-like feature of the platform. The 
sloping anterior aboral margin terminates near the anterior end of the basal cavity. 
On the outer lateral platform, very indistinct node-like denticles may sometimes be 
developed but they are always a relatively inconspicuous feature, though in a very 
few specimens they are barely discernible in both lateral and oral view (e.g. PI. 16, 
figs. 7a-d). 



Gnathodus girtyi simplex Dunn 
Plate 16, figs. ia~4d 



1957 Gnathodus girtyi Hass ; Bischoff : 24, 25, PI. 4, fig. 21 (non PI. 4, figs. 16, 17, 22, 23 = G. 

girtyi girtyi Hass ; non PI. 4, figs. i8-2o = G. girtyi turritus Collinson & Druce. 
1957 Gnathodus girtyi Hass ; Ziegler in Fliigel & Ziegler : 40-41, PI. 3, figs. 6, 9-13, 20., 
1957 Gnathodus bilineatus semiglaber Bischoff ; Ziegler in Fliigel & Ziegler : PI. 3, fig. 22 

(non PI. 3, figs. 5, 8, 14, 2$ = Gnathodus semiglaber). 
1959 Gnathodus texanus Roundy ; Voges : 284-285, PI. 33, figs. 40-43. 
i960 Gnathodus clavatus Clarke (partim) : PI. 4, figs. 7-9 (non pi. 4, figs. 4-6= Gnathodus 

girtyi girtyi Hass) . 
1962 Gnathodus texanus Roundy ; Higgins : PI. 3, fig. 28. 

1962 Gnathodus girtyi Form B Meischner : 31, text-fig. 10. 

1963 Gnathodus girtyi Form A Hass ; Bouckaert & Higgins : 17, text-fig. 3. 
1965 Gnathodus girtyi simplex Dunn : 1148, PI. 140, figs. 2, 3, 12. 

Gnathodus girtyi simplex Dunn ; Collinson & Druce in press. 

Diagnosis. Subspecies of G. girtyi in which lateral denticles on both inner and 
outer lateral margins of platform are more feebly developed than in G. girtyi girtyi 
and are also restricted to anterior and medial parts of platform. 

Material. 260 specimens : figured, X 107, X 108, no, in. 

Range. North Crop CYD 7A-3D 23, Avon Gorge D 26. 

Description. In lateral and aboral views the main features of this subspecies are 
closely similar to those of G. girtyi girtyi especially in the form of the anterior blade 



BRITISH AVONIAN CONODONT FAUNAS ioi 

and of the basal cavity. The most conspicuous difference is in the character of the 
accessory lateral denticles on the posterior platform. The denticles on the inner 
lateral platform are relatively more strongly developed than those on the outer. 
They consist of up to 9 denticles, the highest and most massive being at the anterior 
end, and are separated by a trough from the main median carina. Those towards the 
posterior end of the series tend to be smaller and also to be developed nearer to the 
carina. The denticles of the outer lateral platform are smaller and fewer in number 
and extend further posteriorly than those on the inner lateral platform. In oral view 
both series of lateral nodes converge posteriorly and fuse with the median carina, the 
carina extending further posteriorly than either series of lateral denticles. In lateral 
view the denticles of the inner series approach the height of those on the median 
carina, but are still fractionally shorter. In outer lateral view the denticles at the 
posterior end of the outer lateral series tend to be slightly larger and more con- 
spicuous than those at the anterior end. The apron on the outer lateral platform, 
when seen in oral view, is relatively much more laterally expanded than that of the 
inner lateral platform. The denticles on the inner lateral platform tend to be 
developed in a semi -transverse form, their outer edges being higher than their inner. 
They show semi-radiate development around the central point of the inner lateral 
platform, but this is not strongly marked in all individuals. 

Remarks. This subspecies was recognized as a distinct group by Meischner 
(1962) and Bouckaert & Higgins (1963). 

Gnathodus girtyi soniae subsp. nov. 
Plate 17, figs. 5a-8d 

Derivation of name. After Miss Sonia J. Kostromin. 

Diagnosis. Subspecies of Gnathodus girtyi resembling G. girtyi girtyi in having 
ornamentation developed continuously around posterior platform and encircling 
posterior termination of carina, but differing in development of 1 or 2 low rounded 
inconspicuous nodes on outer-anterior-lateral surface of platform. 

Material. 18 specimens : Holotype X 113, Paratypes X 115, X 112, X 114 
(all figured). 

Type locality and horizon. North Crop. Sample 3D 12. 

Range. North Crop 3D 2-3D 14/15. 

Description. A subspecies of Gnathodus girtyi with greatly expanded apron-like 
posterior platform, the sides sloping sharply down. The median carina is strongly 
developed and its posterior end is completely encircled by the lateral denticles of the 
platform. The inner-lateral parapet is the highest single feature of the platform 
ornament. It begins at a point anterior to the origin of the ornament, on the outer 
lateral side, and has 3 or 4 massive laterally elongate denticles, the highest of which 
tend to be those at the posterior end ; they are separated from the carina by a 
narrow sulcus, which opens anteriorly into a siphonodellid-like spout. The denticles 
decrease posteriorly in size, and are arranged as a linear series of low node-like forms. 



io2 BRITISH AVONIAN CONODONT FAUNAS 

On the outer-lateral margin of the platform one or two low rounded denticles are 
developed. These tend to be developed about midway along the length of the 
platform, and are visible but not conspicuous in lateral view. 

The aboral cavity is large and flared, and the quadrate outline of the outer lateral 
margin of some specimens is strongly reminiscent of G. bilineatus. 

Gnathodus girtyi turritus Collinson & Druce 
Plate 31, fig. 23 

1957 Gnathodus girtyi Hass ; Bischoff : 24, 25, PI. 4, figs. 18-20 [non figs. 16, 17, 22, 23 = 
Gnathodus girtyi girtyi Hass ; non pi. 4, fig. 21 = G. girtyi simplex Dunn). 
Gnathodus girtyi turritus Collinson & Druce in press. 

Material. 5 specimens : figured, X 116. 

Range. North Crop 3D 19-3D 23. 

Description A subspecies of G. girtyi with a low posteriorly reduced carina. 
The lateral denticle ridges are generally continuous around the posterior edge of 
the platform. The sides of the posterior platform are nearly vertical. 

Remarks. The subspecies is extremely rare in our collections. Transitional 
specimens of G. girtyi girtyi are present in faunas from Yorkshire and the North Crop. 
It is difficult to refer these transitional specimens to one or other subspecies with any 
certainty. 

Gnathodus girtyi subsp. nov. A 
Plate 17, figs. ia-3d 

Material. 3 specimens : figured, X 117, X 118, X 119. 
Range. North Crop CYD 7. 

Description. A subspecies of G. girtyi characterized by the development of 1 or 
2 vertical lateral pillars near the anterior inner end of the platform. The pillars 
extend from the oral surface almost to the aboral margin. 

The three specimens upon which this new subspecies is based show the general 
features which are characteristic of G. girtyi girtyi. They differ from that subspecies, 
however, in being left forms in which the longer inner lateral denticulated margin of 
the platform is produced downwards by an unornamented, vertical column. In one 
specimen (PI. 17, figs. 3a-d) this column reaches the aboral margin which is deflected 
by it. In this particular specimen the vertical pillar occurs about one quarter of the 
platform length behind the anterior end of the inner lateral denticle ridge. In the 
specimen illustrated in PI. 17, fig. I, the vertical pillar occupies the same relative 
position but is much less conspicuous, and the lateral margin only is conspicuously 
offset by it. In this specimen the oral margin of the denticulation is not disturbed in 
any way by a development of the lateral pillar. In the specimen shown in PI. 17, 
fig. 2, two sharply angular vertical ridges are developed in the same relative position, 
but neither of these extends into the aboral margin ; between them there is a 



BRITISH AVONIAN CONODONT FAUNAS 103 

regularly " U " shaped concave depression in the lateral face ; their upper termina- 
tions are bluntly pointed, and in this case they are joined to the main ridge of plat- 
form denticles by inconspicuous lateral ridges, although the denticle line is not 
broken by them. The ridge is not denticulated or ornamented in any obvious way 
in any of the three specimens. 

Remarks. It is possible that these three forms are pathological variants of G. 
girtyi girtyi but their restriction to a single sample and the fact that all three are left 
lateral forms makes this seem unlikely. 

Gnathodus homopunctatus Ziegler 
Plate 19, figs. 5a-8d 

1957 Gnathodus commutatus punctatus Bischoff : 24, PL 4, figs. 7-11, 14. 
-non 1957 Gnathodus commutatus punctatus Bischoff ; Ziegler in Fliigel & Ziegler : 40 (PI. 3, 

fig. 16 = juvenile of Gnathodus bilineatus punctatus (Cooper) 1939 ; PL 3, figs. 17, 

24 = Gnathodus sp.). 
J959 Gnathodus commutatus homopunctatus [Ziegler] Voges : 281. 
i960 Gnathodus commutatus homopunctatus Ziegler : 39, 5, PL 4, fig. 3 (nom. nov. for 

Gnathodus commutatus punctatus Bischoff 1957 non Cooper 1939). 

1961 Gnathodus commutatus homopunctatus Ziegler ; Higgins : PL 10, fig. 9, text-fig. ic. 

1962 Gnathodus commutatus homopunctatus Ziegler ; Higgins : PL 2, fig. 21. 
Gnathodus homopunctatus Ziegler ; Collinson & Druce in press. 

Material. 146 specimens : figured, X 120-X 123. 

Range. North Crop CYD 7-3D 14/15. 

Description. There is some similarity and degree of transition between this 
species and G. symmutatus, but the present species differs in having a relatively 
shorter and more symmetrical posterior platform, with the development of more 
conspicuous denticulation. There is some variation in this denticulation ; in 
immature specimens (e.g. PI. 19, fig. 5c) it is barely developed, and is present only as 
rather dark, slightly elevated lateral ridges. In other specimens it tends to be 
arranged at an acute angle to the anterior part of the blade, and consists only of 
short barb-like lines of denticles. In most specimens, however, it forms more or less 
symmetrical lines of low blunt denticles, developed parallel to the outer margin of the 
platform, about midway between its lateral margin and the position of the carina. 
In most individuals the development on the two sides of the carina is equal, but in 
others it is asymmetrical. 

Gnathodus mononodosus sp. nov. 

Plate 19, figs. I3a-i5d 

1 96 1 Gnathodus commutatus var. nodosus Bischoff ; Higgins : PL 10, fig. 7 only, text-fig. ib. 

Derivation of name. From single node on the inner side of cup. 

Diagnosis. Straight to slightly curved blade with subcircular to sub-quad- 
rangular cup, bearing strong, generally elongate node on inner side. 



104 BRITISH AVONIAN CONODONT FAUNAS 

Material. 230 specimens : Holotype X 124, Paratypes X 125, X 126 (all 
figured). 

Type locality and horizon. North Crop. Sample 3D 14/15. 

Range. North Crop CYD 7-3D 19. 

Description. The blade is generally slightly curved. In lateral view both the 
oral and aboral outlines are nearly straight, although the anterior is slightly higher in 
some specimens. The denticles tend to be larger and more distinct at the anterior 
end and become increasingly small and fused toward the posterior. Most are fused 
to their tips. Both ends of the blade are nearly vertical in most specimens. The 
posterior end of the cup may project beyond the blade. 

In oral view the cup is characteristically sub-quadrangular and slightly asym- 
metrical. The inner half bears a single node which is characteristically large and 
elongate but in some specimens round. The blade is typically more than twice the 
length of the cup. 

Remarks. This species is very close to G. nodosus. That it is not merely a 
random variant of nodosus, in which one or the other node is undeveloped, is shown 
by the fact that the single node occurs only on the inner side of the cup. 

The present specimens tend to show all the main forms of variation exhibited in the 
platform by G. commutatus. They also show the rectangular profile of the blade of 
that species when seen in lateral view, and also the relative variation in the curvature 
and termination of the carina on the posterior end of the platform. In a very few 
specimens the outline of the platform is more reminiscent of G. symmutatus, but it 
differs from that species in having the square lateral profile of the blade, the oral 
surface being of more or less uniform height, and not showing the pronounced 
decrease in size of the posterior denticles over most of the length of the platform 
(see p. 108). 

In a few specimens the inner platform is more elongate than in typical members of 
the species, the anterior margin being elongated at right angles to the line of the 
blade. These individuals are further distinguished by the presence of two denticles 
on the inner platform developed in a line lying at about 45 ° to the blade and pointing 
anteriorly, and both being rather laterally compressed and basally confluent but 
with more or less distinct apical tips. These specimens are so close in every other 
respect to those with a single denticle, that there seems no good reason for separating 
them. 

In some specimens the denticle is not fully developed, but is represented by a slight 
swelling occupying the same relative positions on the inner lateral platform, and 
directed at about 45 ° to the anterior portion of the blade. There are transitions 
between this partial development of the denticle and full development of the denticle 
itself. 

Gnathodus nodosus Bischoff 
Plate 19, figs. i6a-20c 

x 957 Gathodus commutatus nodosus Bischoff (partim) : 23-24, PI. 4, figs. 12, 13. 

1957 Gnathodus commutatus nodosus Bischoff ; Ziegler in Fliigel & Ziegler : 40, PI. Ill, fig. 4. 



BRITISH AVONIAN CONODONT FAUNAS 105 

1958 Gnathodus commutatus nodosus Bischoff ; Lys & Serre : 891, PI. 9, figs. 3a, b, 4a, b. 

1961 Gnathodus commutatus var. nodosus Bischoff ; Higgins (partim) : 213, PI. 10, figs. 8 
(non fig. 7) ; text-fig. ib (non figs, in lower left or in uppermost left). 

1962 Gnathodus nodosus Bischoff ; Higgins : PI. 2, fig. 19. 

1962 Gnathodus comm. nodosus Bischoff ; Meischner : 31, text-fig. 10. 

1963 Gnathodus commutatus nodosus Bischoff ; Bouckaert & Higgins : 17, fig. 3. 
Gnathodus nodosus Bischoff ; Collinson & Druce in press. 

Material. 220 specimens : figured, X 509, X 510, X 127, X 128, X 129. 
Range. North Crop 3D 10-3D 22. 

Description. This species shows some characteristics with both G. mononodosus 
and G. commutatus. These include the posteriorly restricted laterally expanded 
sub-circular to asymmetrical platform, and the rectangular lateral profile of the 
uniform blade. The distinctive feature of the present species is the development of 
denticles on both sides of the posterior platform. These are generally unevenly 
developed, the one on the inner lateral side (represented by the concave lateral 
flexure of the blade) generally being the more strongly developed of the two. Where 
the denticles are more strongly developed, they tend to make angles of 45 ° with the 
anterior part of the blade and to be laterally elongate. In some specimens the outer 
lateral denticle is very feebly developed in comparison with the inner, but wherever 
there is a suggestion of such bilateral denticle development, specimens are included 
in the present species. Like the other species referred to above, this species shows 
considerable but continuous variation in the symmetry and degree of lateral expan- 
sion of the posterior platform, the form of the denticles, and the relationship of the 
posterior portion of the carina to the posterior end of the platform ; there is also 
variation in the degree of lateral deflection of the blade, and the outer lateral denticle 
may also be developed posterior to the position of the inner lateral denticle. 

The blade is similar in general form to that of G. commutatus and G. mononodosus, 
having about 15 to 20 regular denticles, fused almost to their tips, and developing 
straight oral and aboral margins. There is a tendency in some specimens for the two 
anterior denticles to be relatively larger than the rest (e.g. PI. 19, fig. 18a). The 
basal cavity is wide and flaring. 



Gnathodus punctatus (Cooper) 
Plate 18, figs, ia-c, ioa-nd 



!939 Dryphenotus punctatus Cooper : 386, PI. 41, figs. 42, 43, PI. 42, figs. 10, 11. 

1939 Dryphenotus litus Cooper : 386, PI. 42, figs. 34, 35. 

J 939 Dryphenotus macrolobus Cooper : 386, PI. 41, figs. 48, 49 ; PL 42, figs. 45, 46. 

1939 Dryphenotus oxys Cooper : 386, PL 42, figs. 12, 13. 

1944 Gnathodus {Dryphenotus) macrolobus Cooper; Branson & Mehl : 245, PI. 94, fig. 69. 

1951 Gnathodus punctatus (Cooper) Hass : 2539, PL 1, fig. 2. 

non 1957 Gnathodus commutatus punctatus Bischoff ; 24, PL 4, figs. 7-1 1, 14. 

1957 Gnathodus bilineatus semiglaber Ziegler in Fliigel & Ziegler : PL in, fig. 23 only. 

non 1957 Gnathodus commutatus punctatus Bischoff ; Ziegler in Fliigel & Ziegler : 40, PL 111, 
figs. 16, 17, 24. 

J 959 Gnathodus punctatus (Cooper) Hass : 395, PI. 47, figs. 11-18. 



io6 BRITISH AVONIAN CONODONT FAUNAS 

1959 Gnathodus punctatus (Cooper) Voges : 283-284, PI. 33, figs. 34-37. 

i960 Gnathodus punctatus (Cooper) Kronberg, Pilger, Scherp & Ziegler : PI. 4, figs. 15-18. 

1963 Gnathodus punctatus (Cooper) Ziegler : PI. 2, fig. 4. 

Material. 13 specimens : figured, X 131, X132, X 133. 

Range. Avon Gorge Samples Z 33-38. 

Description. This species is characterized by the adult specimens having the 
nodes of the inner and outer sides of the platform fused with those of the carina in the 
posterior two thirds of the platform. The pattern of nodes on the platform is also 
characteristic, there being four rows, radiating from the junction of the platform and 
blade. The platform is asymmetrical, being widest at the anterior end and pointed 
at the posterior ; the outer side is wider than the inner. In juvenile examples the 
carina is high, but in adult specimens the carina is fused with a row of nodes on the 
inner and outer sides of the platform. A double row of nodes is present on the outer 
side in fairly juvenile examples, but frequently there is only one row of nodes 
developed on the inner side in juveniles. The blade is slightly longer than the 
platform. 

Remarks. Hass (1959) has illustrated growth stages of this species. The 
specimens obtained in the present study most closely resemble those figured by Hass 
in PI. 47, figs. 12, 13. Typically, the smaller inner side of the platform bears one 
node, whereas the wider outer side of the platform has a few scattered nodes. The 
outer side of the platform extends to the posterior tip of the unit. The inner side of 
the platform does not extend to the posterior tip of the unit, but extends further to 
the anterior than does the outer side of the platform. 

In North America Gnathodus punctatus is abundant in the middle faunal zone of 
the Chappel Limestone, and also occurs in the Siphonodella cooperi and Bactro- 
gnathus communis zone. In the Avon Gorge it is characteristic of the Z 2 beds. 

Gnathodus semiglaber Bischoff 
Plate 30, fig. 1 

1947 Gnathodus perplexus (Branson & Mehl) Mehl & Thomas : 10, PI. 1, fig. 4. 

1957 Gnathodus bilineatus semiglaber Bischoff : 22, PI. 3, figs, ia, b, 2-10, 12-14. 

1957 Gnathodus bilineatus semiglaber Bischoff ; Ziegler in Fliigel & Zeigler : p. 38, 1. pi 11, 

figs. 5, 8, 14, 19 only (non pi. in, fig. 23 = Gnathodus punctatus, PI. IV, fig. 11, non PI. 3, 

fig. 22 = Gnathodus girtyi simplex Dunn). 
1959 Gnathodus semiglaber Bischoff ; Voges : 285, PI. 33, figs. 38, 39. 
i960 Gnathodus semiglaber (Bischoff) Ziegler in Kronberg, Pilger, Scherp & Ziegler : PI. 4, 

figs. 3-6. 
1962 Gnathodus semiglaber (Bischoff) Collinson, Rexroad & Scott : 10, 22, Chart 3. 
1962 Gnathodus semiglaber (Bischoff) Higgins : 13, PI. 3, fig. 26. 
1962 Gnathodus semiglaber (Bischoff) Miiller : 1388, fig. 1. 
1962 Gnathodus semiglaber (Bischoff) Meischner : 31, text-fig. 10. 
1964 Gnathodus semiglaber (Bischoff) Rexroad & Scott: 30, PI. 2, figs. 1, 2. 

Material. 3 specimens : figured, X 421. 
Range. Avon Gorge Z 28-Z 30. 



BRITISH AVONIAN CONODONT FAUNAS 107 

Description. This species, which is well known and widely distributed in both 
Europe and North America, is characterized by a low, small parapet on the inner side 
of the platform, and a few scattered nodes developed on the middle part of the low 
outer side of the platform. The carina tends to be laterally expanded in the posterior 
part of the platform. Our specimens of this species agree closely with those described 
by other authors. 

Gnathodus simplicatus sp. nov. 
Plate 8, figs. 5a-c. Plate 18, figs. 2a-5b 

1957 Spathognathodus subrectus Holmes ; Fliigel & Ziegler : 53, PI. 11, fig. 12. 
i960 Spathognathodus strigosus Branson & Mehl ; Dvorak & Freyer : PI. 1, fig. 17. 

Derivation of name. From the simple form. 

Diagnosis. A species showing Spathognathodus-Gnathodus transition, with 
characteristic anterior blade, its highest point being at or near the anterior end, and 
with oral surface sloping regularly towards the posterior end of unit. Platform very 
feebly developed. 

Material. 105 specimens : Holotype X 89, Paratypes X 88, 90, 91, 415 (all 
figured). 

Type locality and horizon. North Crop. Sample ZLA 33. 

Range. North Crop ZLA 15-ZLA 33, Avon Gorge Z 33-Z 38. 

Description. The unit is slightly bowed and slightly arched, highest in the 
anterior quarter, and sloping posteriorly. The anteriormost one to three denticles 
may be slightly shorter than the penultimate denticles, but otherwise the oral 
outline is straight to slightly convex. The denticles, which number 13 to 15, are 
small and laterally compressed with free chevron tips. The basal cavity is situated 
in the posterior half and runs to the posterior termination ; the lips flare over the 
whole length and the cavity widens to the mid-point where it becomes constricted 
and then runs as a narrowing groove towards the anterior. The basal margin is 
lipped and slightly stepped in lateral view. 

Remarks. Middle and Upper Devonian forms similar to those described above 
have been named as Spathognathodus bidentatus by Bischoff and Ziegler (1957) and 
Freyer (1961). Bischoff and Ziegler's specimens have a greater number of denticles 
(about 17 total) than ours, and the cavity is different, not quite reaching the posterior 
end, and being greatly flared anteriorly. Freyer's specimens have only about 10 
denticles and are much lower towards the posterior. 

The present species is transitional between Spathognathodus and Gnathodus, but is 
included in Gnathodus because the basal cavity is developed posteriorly, is longi- 
tudinally extended, and the lips show a tendency to lateral flare. 

There is some similarity between the forms described here andS. cristulus, which is 
considered by American workers to be the basic stock for all spathognathodid 
lineages. It is possible that the two species are the root stocks for successive 
gnathodid developments, the genus Gnathodus being polyphyletic 



io8 BRITISH AVONIAN CONODONT FAUNAS 

In a few specimens the highest denticles are developed above the anterior end of 
the basal cavity (e.g. PI. i8, fig. 2c ; X 89). In all other respects, however, these 
specimens resemble the holotype. 



Gnathodus symmutatus sp. nov. 
Plate 19, figs. ia-4c 

? 1941 Spathognathodus commutatus Branson & Mehl ; Ellison & Graves : PI. 2, fig. 4 [non 

PI. 2, fig. 6). 
? 1956 Spathognathodus cf. inornatus Hass ; Elias : PI. 3, figs. 62, 65 {non PI. 3, figs. 41, 42). 
1958 Gnathodus commutatus commutatus Branson & Mehl ; Lys & Serre : 891, PI. 9, figs. 
2a, b. 

Material. 42 specimens : Holotype X 134, Paratypes X 135-7. 

Type locality and horizon. North Crop Sample 3D 14/15. 

Range. North Crop CYD 7-3D 22. 

Diagnosis. Small gnathodids with elongate blades, and relatively little expanded 
posterior platforms, convex in outline, tapering at both ends, and unornamented. 

Description. The blade is more or less regular in height or has a gently convex 
oral profile in the anterior portion, but for most of the length of the platform the 
denticle height decreases uniformly towards the posterior end of the unit. In 
mature specimens the anterior blade occupies about half of the total length of the 
unit ; it is often deepest at its posterior end, and the oral surface bears about 9 or 10 
denticles anterior to its junction with the posterior platform. These denticles tend 
to be more or less erect, discrete from about their mid points upwards, and sharply 
pointed ; they are strongly laterally compressed and are of sub-equal size, the 
largest tending to occur in the posterior portion of the anterior blade. The lateral 
faces of the bar are gently convex and the anterior aboral margin is rounded to 
bluntly angular ; the anterior edge is straight, and the bar is straight or gently 
deflected in a horizontal plane. The blade is continued posteriorly as a central 
carina on the platform, the denticles being short, and partly fused ; the total number 
of denticles in the blade and the carina is about 22. The posterior platform occupies 
the posterior half to two-thirds of the unit ; it is relatively unexpanded laterally 
and tapers uniformly at its anterior and posterior ends. It tends to be steep sided, 
the lateral faces forming an acute angle below the carina ; one face is often more 
strongly laterally expanded than the other. The surface is smooth and no ornamen- 
tation is developed, although in some specimens there is a tendency for the appear- 
ance of incipient marginal denticulation, similar to that in G. homopunctatus. 

The basal cavity is wide and flaring, and is continued anteriorly as a narrow groove 
on the base of the anterior blade. The growth of the posterior platform in mature 
specimens tends to reduce the angle which its lateral faces form at their junction. In 
most specimens its depth is about equal to the height of the carina on its surface. 



BRITISH AVONIAN CONODONT FAUNAS 109 

Gnathodus ? sp. nov. 
Plate 18, figs. 7a-c 

Material, i specimen : figured, X 92. 

Locality and horizon. North Crop. Sample ZL 8. 

Range. North Crop ZL 8. 

Description. A gnathodid ? with transversely ridged posterior half of platform ; 
anterior part of platform unornamented except for marginal nodes. Base deeply 
excavated. Anterior bar unknown. 

The anterior blade is broken but the platform is preserved. The carina consists 
of a row of low nodes ; in the posterior half of the platform, a row of smaller nodes 
runs either side of the carina, with which they fuse to give a series of trinodate 
transverse ridges. The inner platform is expanded slightly more than the outer, and 
both are unornamented, except for a short marginal row of fused nodes occurring in 
the anterior half and diverging posteriorly. 

In aboral view the cavity occupies the whole area of the platform and is grooved 
along its mid-length. 

Remarks. This species is unlike any described gnathodid and does not bear any 
obvious phylogenetic relationship to other species. 



Gnathodus sp. 

Plate 17, figs. 4a-d 

Material, i specimen : figured, X 138. 

Range. Scotland HOSIE 2A. 

Description. A single specimen of Gnathodus appears to be close to G. girtyi, but 
differs from it in the character of the lateral denticles of the posterior platform. In 
the present specimen the development on the two lateral areas of the platform is 
highly asymmetrical, and the platform of the inner-lateral margin, which begins 
anterior to the point of origin of that on the outer-lateral margin, is short, and 
consists of only three or four fused blunted denticles. Just anterior to its fusion 
with the carina, a less conspicuous fused, inner series of lateral denticles is developed 
on the outer-lateral platform. These become confluent with the carina just in front 
of its posterior termination, but do not reach the posterior end of the carina. The 
apron is wide and flaring, and is asymmetrical in both oral and aboral views. In 
lateral view the denticles of the anterior blade are sharp and erect, and those of the 
carina are also sharply tipped and distinct, standing higher than the lateral denticles 
on either side of the platform. The denticles of the inner lateral process form 
blunted parapet-like nodes in lateral view. The denticles of the carina decrease 
rapidly in size towards the posterior in the posterior half of the platform. 



no BRITISH AVONIAN CONODONT FAUNAS 

Genus HIBBARDELLA Ulrich & Bassler 1926 

1925 Hibbardella Bassler ; 219 (nom. nud.). 

1926 Hibbardella Ulrich & Bassler : 37. 

Type species. Prioniodus angulatus Hinde 1879. 

Description. Ulrich & Bassler established the genus Hibbardella with the type 
species Hibbardella (Prioniodus) angulata Hinde for a group of arched blade-like 
conodonts in which a striking apical denticle was developed. The whole structure 
was bilaterally symmetrical and the apical denticle sharp-edged, erect and greatly 
elongated. The denticles of the anterior bar were relatively few in number, widely 
spaced and turned slightly inward. Ulrich & Bassler did not mention the character 
of the basal cavity, nor the possibility of the development of a denticulated posterior 
bar. Topotype material studied by Dr. J. W. Huddle, of which he has kindly 
provided us with photographs, shows that both these features are well preserved. A 
more or less short stout denticulated posterior bar is developed, and there is a thin 
groove-like basal cavity which extends along both the anterior bars and the posterior 
bar. 

Subsequent authors have erected several genera of essentially similar general form 
which have been distinguished on minor morphological differences. These include 
Roundya Hass (1953) Ellisonia Muller (1956) and possibly also Diplododella Bassler 
(1925). There has been some discussion as to the validity of these and other genera, 
especially the genus Trichonodella. The most satisfactory solution to the present 
situation seems to be to subdivide the genus Hibbardella into three subgenera, based 
on the following characteristics : 

1. HIBBARDELLA s.s. arched denticulated conodonts, with a bilaterally 
symmetrical anterior bar and a strongly developed apical denticle. The 
apical denticle is strongly compressed antero-posteriorly and has sharp 



Mam cusp 



Denticles 



Lateral bar 



Posterior bar 




Laterol bar 



Position of basol cavity 



Anterior view 



Fig. 23. Hibbardella sp. showing morphological terms used in the text. 



BRITISH AVONIAN CONODONT FAUNAS in 

lateral edges. The basal cavity is small and restricted to the aboral surface 
of the apical denticle, but aboral grooves are developed on both the anterior 
and the posterior bars. There is a short stout denticulated posterior bar, 
which bears a series of discrete denticles. 

Type species. Prioniodns angulatus Hinde 1879. 

2. ROUNDYA conodonts of similar overall form to Hibbardella s.s. but charac- 

terized by distinctive basal cavities and by the form of the apical denticle. 
The basal cavity is relatively much larger than that of Hibbardella, although 
it is still confined to the lower surface of the apical denticle. The whole 
aboral surface of that denticle is hollowed out, but the cavity does not flare 
beyond its basal area. The denticle itself is characterized by its distinctive 
cross-section. In its lower half it is broadly sub-circular and robust in form, 
the posterior surface having a longitudinal broad concave cavity which is 
deepest at the proximal end, and decreases in depth towards the mid-length 
of the denticle. The lateral faces of the apical denticle are smooth and 
strongly convex, but in their medial areas a conspicuous groove is developed 
longitudinally in the lower part. From this a strong lateral costa develops 
on each lateral face. In the distal half of the apical denticle it becomes 
strongly anterio-posteriorly compressed, but the lateral edges remain sharp, 
and the anterior and posterior faces broadly convex. 

Type species. Roundya barnettana Hass 1953. 

3. HASSOGNATHUS subgen. nov. conodonts whose general form is similar to 

Hibbardella, but which are characterized by the fact that the anterior bars 
are essentially unexcavated, their aboral surfaces being shallow, concave, 
depressions. The basal cavity is conspicuous, but is largely developed 
below the posterior bar, although it extends and is continuous with one 
below the apical denticle. The apical denticle is usually sub-circular in 
cross-section and unornamented. The whole appearance of members of 
this subgenus is of a Ligonodina which has developed an additional lateral 
bar. 

Type species. Trichognathus separata Branson & Mehl 1934. 



Subgenus HIBBARDELLA (HIBBARDELLA) Ulrich & Bassler 1926 

Hibbardella (Hibbardella) abnormis Branson & Mehl 

Plate 31, fig. 6 

1940 Hibbardella abnormis Branson & Mehl : 184, PI. 6, fig. 14. 

1963 Hibbardella abnormis Branson & Mehl ; Rexroad & Collinson 10, PI. 2, figs. 15, 18, 20, 21. 

1965 Hibbardella abnormis Branson & Mehl ; Rexroad & Collinson : 9, PI. 1, figs. 8, 9. 



ii2 BRITISH AVONIAN CONODONT FAUNAS 

Material. 3 specimens : figured, X 508. 
Range. North Crop CYD 7-3D 8. 

Description. Rexroad & Collinson (1963) have shown that the holotype of this 
species is broken and that the limbs are longer than the original description suggests. 

The present specimens are fragmentary, but they show the specific characteristics. 
The posterior bar tends to be rather strongly developed, and the lateral bars are 
sharply flexed posteriorly. 



Hibbardella (Hibbar delta) acuta Murray & Chronic 
Plate 25, figs, iga-20 

1961 Hibbardella fragilis Higgins : 213, PI. 12, fig. 4, text-fig. 2. 
1963 Hibbardella fragilis Higgins ; Bouckaert & Higgins : 17, fig. 3. 
1965 Hibbardella acuta Murray & Chronic : 598, PI. 73, figs. 3-5. 
Hibbardella higginsi Collinson & Druce in press. 

Material. 19 specimens : figured, X 139, X 422. 
Range. North Crop 3D 4-3D 17. 

Description. The most distinctive features of this species are the greatly 
elongated anterior and posterior bars, the relatively slender denticulation and the 
lateral twisting of the anterior bars. The apical denticle, although relatively long, is 
only about half the length of the anterior bars ; it is slender, with a feebly convex to 
flat anterior face and sharp lateral edges ; the posterior part of the face of the apical 
denticle is developed into a posterior knife edge, the posterior lateral faces tending to 
be rather flat. The anterior bars are long and are longitudinally twisted so that the 
denticles tend to originate from the anterior surface. The bars bear up to 10 lateral 
denticles which are basally confluent but apically distinct and are more or less com- 
pressed anterior-posteriorly. In addition to their longitudinal flexure, the bars are 
recurved posteriorly, so that their anterior faces are gently convex. They diverge 
from each other at an angle of about 30 °. 

The posterior bar is elongated and decreases in depth posteriorly. Its aboral 
margin is gently concave, most of the curvature being concentrated near the mid- 
point of the unit. Its oral surface bears a series of confluent, but apically distinct, 
hindeodellid-type denticles. The larger members of the series tend to increase in 
size toward the mid-point of the bar, and then to decrease toward the posterior end. 
There are about 8 or 9 main denticles, each separated by two or three smaller 
denticles. The denticles are more or less laterally compressed, but tend to have 
rather strong convex lateral faces. The lateral faces of the posterior bar are gently 
convex. The whole appearance of the posterior bar is strikingly deep and elongated. 

Shallow longitudinal slit-like grooves extend along the anterior and posterior bars, 
and there is a very small pit below the apical denticle. 



BRITISH AVONIAN CONODONT FAUNAS 113 

Hibbardella (Hibbardella) milleri Rexroad 
Plate 25, figs. 23a-25b 

1957 Hibbardella n. sp ? Rexroad : 31, PI. 1, fig. 19. 

1958 Hibbardella milleri Rexroad : 18, PI. 2, figs. 13-16. 
i960 Hibbardella milleri Rexroad ; Clarke : 6, PI. 1, fig. 6. 
1961 Hibbardella milleri Rexroad ; Higgins : PI. 12, fig. 7. 

1961 Hibbardella milleri Rexroad ; Rexroad & Burton : 1153, PL 140, figs. 3, 4. 

1964 Hibbardella milleri Rexroad ; Rexroad & Furnish : 671, PI. 111, fig. 17. 

1965 Hibbardella milleri Rexroad ; Rexroad & Nicoll : 19, PI. 1, fig. 13. 

Material. 3 specimens : figured, X 140, X 141, X 142. 
Range. North Crop 3D 14/15. 

Description. Individual specimens of this species bear a strong resemblance to 
those described by Rexroad, but differ from his description in having no denticle 
developed anterior to the apical denticle. The most characteristic features of 
individuals are the short, deep and obtusely divergent anterior bars, the distal ends 
of which are spatulate to sharply pointed. The denticles of the anterior bars are 
massive, increasing in size distally and numbering 3 or 4. They are more or less 
anteriorly compressed and sharp edged. The apical denticle is massive, elongate, 
sub-circular to oval in cross-section ; in some specimens it is very elongate (e.g. 
PL 25, fig. 24). In well preserved specimens the apical denticle is sharply pointed at 
its distal end, and is sub-circular in cross-section. In the proximal third its posterior 
surface is marked by either a very faint groove or a very faint depression. The 
posterior bar is short, narrow and deep, with two or three small, isolated denticles on 
its oral surface. 

The basal cavity is developed as shallow grooves which run along the posterior and 
the anterior bars, and the base of the apical denticle is slightly excavated. The 
aboral groove does not extend the whole length of the anterior bars, and the posterior 
groove decreases in width and depth posteriorly. 

Hibbardella (Hibbardella) ortha Rexroad 
Plate 25, figs. 22a, b 

1900 Prioniodus angulatus Hinde (partim) : 343, PI. 10, fig. 18 (non fig. 19). 
non 1926 Hibbardella angulata (Hinde) Ulrich & Bassler : 37, PI. 3, figs. 1-4. 
1928 Hibbardella angulata (Hinde) ; Holmes : 11, PL 4, fig. 32. 



1958 Hibbardella ortha Rexroad 
i960 Hibbardella ortha Rexroad 
1961 Hibbardella ortha Rexroad 

1964 Hibbardella ortha Rexroad 

1965 Hibbardella ortha Rexroad 
Hibbardella ortha Rexroad 



18, PL 2, figs. 9-12. 

Clarke : 6, PI. 1, fig. 7. 

Rexroad & Burton : 1153, PL 140, figs. 5, 6. 

Rexroad & Furnish : 671, PL 111, fig. 16. 

Rexroad & Nicoll : 19, PL 1, fig. 12. 

Collinson & Druce in press. 



Material. 780 specimens : figured, X 143. 

Range. North Crop 3D 10-3D 22. 

Description. The present specimens are more complete than those described by 



ii 4 BRITISH AVONIAN CONODONT FAUNAS 

Rexroad, but they agree in all the essential details with his description. Their most 
striking features are the deep and strongly antero-posteriorly compressed anterior 
bars, which diverge from each other at an angle of about 130 °. They are relatively 
short, and bear on their oral surfaces up to 6 discrete and sharply pointed denticles. 
The two nearest the apical denticle and the distal denticle on each bar are small, but 
the three intervening denticles are larger and tend to increase in size distally. The 
ends of the anterior bar are bluntly spatulate, and the aboral margin is straight to 
feebly convex. The anterior face of the apical denticle is convex, the apical denticle 
itself being about twice the length of the largest denticle of the anterior bar, slender 
and pointed ; it tends to have rather feeble anterior lateral edges in its lower portion, 
but becomes sub-oval in cross-section towards its distal end. Both it and the 
denticles of the anterior bar tend to stand rather erect to the bar itself and are not 
obviously posteriorly recurved, although the denticles of the lateral bar tend to be 
inwardly curved towards the apical denticle. 

The posterior bar is long, slender, strongly laterally compressed and relatively deep. 
It has feebly convex lateral faces, and bears a series of up to 6 crowded, but apically 
discrete, laterally compressed, short denticles on its oral surface. A small pit below 
the apical denticle extends posteriorly as a faint groove along the posterior bar, and 
also along the proximal portions of the anterior bars. The posterior margin of the 
apical denticle is sharp-edged. Beneath the apical denticle the posterior-aboral 
margin of the anterior bar is excavated by an indented depression to join the basal 
margin of the posterior bar. 

Hibbardella (Hibbardella) parva sp. nov. 
Plate 25, figs. 21a, b 

Diagnosis. Hibbardellid with very small, delicate structure ; anterior bars 
flexed forwards diverging in vertical plane at a very obtuse angle. At their junction 
deeply indented aborally on anterior margin. Posterior bar strong ; apical denticle 
elongate, strongly laterally compressed. Basal cavity minute or non-existent. 

Material. 5 specimens : Holotype X 144 (figured). 

Type locality and horizon. North Crop. Sample 3D 14/15. 

Range. North Crop 3D 14/15. 

Description. The anterior bars are relatively deep, short and laterally com- 
pressed, and each bears about 5 oral denticles. They diverge anteriorly in a 
horizontal plane, so that the angle between them in a horizontal plane is about 90 °. 
They are little flexed in a vertical plane, and the angle between them is very obtuse. 
The aboral surface has a concave general appearance. This anterior curvature is 
most obvious in aboral view. It is relatively inconspicuous in oral view, where it is 
obscured by the development of the apical denticle, nor is it continued along the 
medial and distal parts of the bars which tend to straighten out and lie in a single 
plane relative to one another. 

Remarks. This species is closest to H. (H.) ortha Rexroad 1958, but it differs in 



BRITISH AVONIAN CONODONT FAUNAS 115 

the distinctive form of the apical denticle, and in the characteristic angle of the 
anterior bars as seen in the vertical plane. In H. (H.) ortha this angle approaches 
90 ° but it is nearer 180 ° in H. (H.) parva. H. (H.) ortha also lacks the strong 
posterior recurvature of the apical denticle and the denticles of the anterior bar. 

Hibbardella (Hibbardella) cf. macrodentata Thomas 
Plate 25, figs. i6a-i8c 
1949 Hibbardella macrodentata Thomas : 422, PI. 4, fig. 25. 

Material. 75 specimens : figured, X 147, X 148, X 146. 

Range. North Crop KL 2-ZLA 33, Avon Gorge K3-Z 38. 

Description. The apical denticle is tall, laterally compressed and inclined 
posteriorly. The anterior arch is deep with each limb curved posteriorly. The 
anterior bars diverge at an angle of approximately 90 °, and the aboral edge of the 
anterior bars is lower than that of the posterior bar. The denticles of the arch are 
isolated, sub-circular and of unequal height. The posterior bar is narrow, long 
(though broken in the majority of our specimens) and finely denticulate. All the 
denticles are sub-circular and posteriorly inclined. The cavity is minute and 
situated beneath the apical denticle. 

Remarks. The holotype is broken, but, from Thomas's illustration and description 
it would appear that our specimens are very close to H. macrodentata. Although 
Thomas describes the posterior bar as blunt and non denticulate, the holotype 
(shown in PI. 4, fig. 25) is clearly broken. 

Hibbardella (Hibbardella) sp. 

Plate 25, figs. 15a, b 

Material, i specimen : figured, X 441. 
Range. North Crop KL 16. 

Description. This specimen is characterized by the massive form of its anterior 
bars. The anterior bars are short, deep and strongly downcurved, their oral and 
aboral margins being strongly convex in anterior view, although there is a conspic- 
uous indentation in the aboral profile below the apical denticle. The strongest 
downflexing is in the distal thirds of the bars. The lateral faces of the anterior bars 
are convex, and both are characterized by prominent longitudinal ridges developed 
just below mid-height, and extending along the length of the bars. The oral surfaces 
of the anterior bars bear up to six discrete and rather stout denticles, the largest being 
in the medial portions of the bars. They are discrete, more or less rounded in cross- 
section, and the larger ones are slightly inflexed towards the apical denticle. Their 
length is unknown, but the largest is longer than the depth of the basal bars. The 
ends of the bar are spatulate. 

The apical denticle is relatively slender, being only slightly greater in width than 
the largest of the denticles of the anterior bars. The anterior face is rounded, but 



n6 BRITISH AVONIAN CONODONT FAUNAS 

the posterior face is blunt and has a median groove. The apical denticle in posterior 
view is widest at the oral edge of the bar and tapers uniformly to the tip. 

The aboral surface is sharp, being broken only by a small triangular shaped pit 
directly beneath the apical denticle. 

Subgenus HIBBARDELLA (ROUND Y A) Hass 1953 
Type species. Roundya barnettana Hass 1953. 

Hibbardella (Roundya) barnettana Hass 
Plate 25, figs. 2a-5b 

1953 Roundya barnettana Hass : 89, PI. 16, figs. 8, 9. 

1957 Roundya barnettana Hass ; Bischoff : 52, PI. 5, figs. 19, 20. 

1958 Roundya costata Rexroad : 26, PI. 2, figs. 5-8. 

1961 Roundya subacoda (Gunnell) Higgins : 220, PI. n, fig. 13. 

1961 Roundya costata Rexroad ; Rexroad & Collinson, PI. 1. 

1962 Roundya subacoda (Gunnell) Higgins : 11, PI. 1, fig. 1. 

1962 Roundya barnettana Hass ; Collinson, Scott & Rexroad : 12. 

Material. 14 specimens : figured, X 151, X 152, X 153, X 154. 
Range. North Crop 3D 14/15, Avon Gorge Z 38-C 15. 

Description. Individuals of the present species agree closely with the very 
detailed description given by Hass (1953 : 89). They are characterized particularly 
by the massive apical denticle, with longitudinal grooves and lateral keels which are 
very prominent in the proximal portion, and sharp lateral edges which are prominent 
in the distal half. There is a conspicuous posterior concave longitudinal depression 
in the proximal quarter of the apical denticle, which becomes obsolescent towards the 
mid-point. The denticle is strongly recurved in its lower portion, but its distal 
portion is straight. The anterior bars are broken in the present specimens, but 
appear massive and bear more than two isolated denticles, which are sub-circular in 
cross-section, and curve upwards to parallel the apical denticle. The anterior bars 
diverge at an angle of about 7o°-8o° in the vertical plane, and the junction between 
them is rounded in anterior view. They shallow distally. The posterior bar is 
broken in the present specimens, but is clearly massive with flat to gently convex 
lateral faces, and has a convex upper surface which bears more than one erect, 
massive, sub-circular denticle. 

The aboral surface of the apical denticle is deeply excavated and the excavation 
continues along the anterior end of the posterior bars. 

Hibbardella (Roundya) sp. 

Plate 25, fig. 1 

Material. 2 specimens : figured, X 423. 
Range. North Crop ZLA 32. 



BRITISH AVONIAN CONODONT FAUNAS 117 

Description. The anterior arch is broken but appears to be formed by aboro- 
lateral extensions of the basal cavity. The apical denticle is recurved posteriorly ; 
it has a convex anterior margin, lateral keels, and a concave posterior depression, 
becoming obsolescent toward the anterior arch. The posterior bar is formed by an 
extension of the posterior lip of the basal cavity and bears at least one inclined 
denticle. 

The basal cavity is large, the aboral region of the apical denticle being completely 
excavated. 

Subgenus HIBBARDELLA (HASSOGNATHUS) nov. 
Type species. Trichognathus separata Branson & Mehl 1934. 

Hibbardella (Hassognathus) separata (Branson & Mehl) 

Plate 25, figs. I3a-i4 

1934 Trichognathus separata Branson & Mehl : 290, PI. 23, fig. 30. 

1934 Trichognathus breviolata ? Branson & Mehl : 291, PI. 23, fig. 29. 

1938 Trichognathus separata Branson & Mehl ; Branson & Mehl : PI. 33, fig. 42. 

1939 Trichognathus separata ? Branson & Mehl ; Cooper : 421, PI. 46, figs. 45, 49. 

1944 Trichognathus separata Branson & Mehl ; Branson & Mehl, in Shimer & Shrock : 243, 

PI. 93, fig. 72. 
1944 Trichognathus separata Branson & Mehl ; E. B. Branson : PI. 32, fig. 42. 
1959 Roundya sp. B Hass : 385, PI. 46, fig. 11. 

Material. 58 specimens : figured, X 150, X 149. 

Range. North Crop KL 19-ZLA 27, Avon Gorge K 21-C 17. 

Description. The posteriorly recurved apical denticle is tall and ovate in cross- 
section, being thickest at the anterior. The anterior arch is short with the anterior 
bars diverging at about 120 °. The bars are narrow, each bearing 3 to 4 short, sub- 
circular posteriorly inclined denticles. The posterior bar is relatively long, being 
thick at the anterior end, and becoming much thinner over the posterior half, where 
it bears a few fine posteriorly inclined denticles. 

In aboral view the unit is excavated, with a large cavity occurring beneath the 
apical denticle and extending along the posterior bar, but becoming gradually 
narrower and ending abruptly. A faint groove runs for a short distance from the 
cavity along either limb of the anterior arch. 

Remarks. The large basal cavity distinguishes this species from H. macro- 
dentata. 

Hibbardella (Hassognathus) ? sp. 
Plate 31, fig. 3 
Material, i specimen : figured, X 319. 
Range. Scotland DUN yy. 



n8 BRITISH AVONIAN CONODONT FAUNAS 

Description. The present specimen is fragmentary but has a very distinctive 
appearance. The posterior bar is elongated and tapers towards the posterior end. 
The main cusp is strongly recurved and strongly laterally compressed in its distal 
half, the proximal half tending to be more rounded. Posterior to it there is a denticle 
adding about a third of the total length of the main cusp, and the denticles posterior 
to this decrease in size posteriorly. They are short, bluntly pointed and discrete. 
The aboral surface of the posterior bar is straight, and the oral surface curves down 
to meet it. The two lateral bars are developed well in front to the line of the main 
cusp, so that the general appearance of the unit in lateral view resembles that of a 
Ligonodina. They are not down-flexed and their aboral margin is in line with that of 
the posterior bar. They make an angle of about 90 ° with the posterior bar in a 
horizontal plane. They share a single short, but stout, recurved denticle, which lies 
directly anteriorly to the main cusp. 

The aboral surface of the posterior bar is excavated by a wide elongate depression. 
The whole margin tapers towards the posterior end. There is no conspicuous cavity 
below the main cusp. 

Remarks. One distinctive feature of this specimen is the presence of the denticle 
anterior to the main cusp. This might ultimately justify the recognition of speci- 
mens of this kind as a new genus, but our present material is inadequate to provide a 
full description. Other fragmentary, but different, hassognathids have a much 
greater stratigraphic range. 

Genus HINDEODELLA Ulrich & Bassler 1926 

1925 Hindeodella Bassler : 219 (nom. nud.). 

1926 Hindeodella Ulrich & Bassler : 38-41. 

Type species. Hindeodella subtilis Ulrich & Bassler 1926. 

Hindeodella antecomplex Collinson & Druce 
Plate 28, figs. 25, 28 
Hindeodella antecomplex Collinson & Druce in press. 

Material. 7 specimens : figured, X 157, X 156. 

Range. North Crop 3D 4-3D 17. 

Description. The present specimens agree closely with the description given by 
Collinson & Druce. The most striking features of the specimens are their small size, 
the general form of the main denticle, which is relatively massive in relation to the 
general size of the unit, being curved posteriorly and inwardly with a very convex 
interior antero-lateral face. The denticles of the posterior bar range up to about 10 
in number, and the two massive posterior denticles are very prominent in lateral 
view. The denticles show a general increase in size posteriorly, as does the depth of 
the posterior bar. The aboral margin of the posterior bar is straight, and each of its 
aboral lateral surfaces is marked by a flange-like structure. The anterior lateral 



BRITISH AVONIAN CONODONT FAUNAS 



119 



process is short, and bears two oral denticles. It is strongly depressed vertically and 
strongly indexed, forming a right angle in its lateral curvature with the posterior bar 
when viewed from above. The aboral surface of the unit is excavated by a narrow, 
shallow, groove. 



Hindeodella brevis Branson & Mehl 
Plate 31, fig. 17 

1934 Hindeodella brevis Branson & Mehl : 195, PI. 14, figs. 6, 7. 

1934 Hindeodella cf. brevis Branson & Mehl : PI. 14, fig. 12. 

1956 Hindeodella brevis Branson & Mehl ; Bischoff & Ziegler : 147, PI. 14, figs. 10, 11. 

1957 Hindeodella brevis Branson & Mehl ; Bischoff : 26, 27, PI. 6, fig. 24. 

Material. 17 specimens : figured, X 514. 

Range. Avon Gorge K 2-Z 38, North Crop 3D 14/15-3D 22. 

Description. The posterior bar is short, deep, straight and relatively thick at its 
oral edge. It bears on its oral surface four or five major denticles, which increase in 
size posteriorly. They tend to be straight, strongly biconvex in cross-section, and 
only slightly inclined posteriorly. Each is separated by up to 3 smaller denticles, 
which are crowded but discrete. The anterior bar is relatively long, and is bent 
almost at right angles to the posterior bar. Its oral surface bears up to 7 short 
denticles, which decrease in size posteriorly. Each of these major denticles of the 
anterior process tends to be separated by a single smaller denticle. The posterior 
bar is excavated by a shallow groove in its anterior portion, and this flares somewhat 
below the main denticle. 



Denticles of 
posterior bar 



Posterior 




Apical denticle 



Anterior bar 

Anterior 



Posterior bar 



Position of basal cavity 
A boral edge 

Fig. 24. Hindeodella sp. showing morphological terms used in the text. 



120 BRITISH AVONIAN CONODONT FAUNAS 

Hindeodella cooperi (Elias) 
Plate 31, figs. 18, 19 

1956 Hamulosodina cooperi Elias : 109, PI. 1, figs. 28, 29. 

Hindeodella cooperi (Elias) ; Collinson & Druce in press. 

Material. 2 specimens : figured, X 159, X 158. 
Range. North Crop 3D 14/15. 

Description. The original description of this species is scarcely adequate to 
differentiate it from several others of the genus Hindeodella. The most distinctive 
features of the present specimens, and also of the specimens shown in Elias' illustra- 
tions, are the greatly elongated posterior bar, the more or less subequal character of 
the denticulation, and the character of the antero-lateral process. The height of the 
denticle is consistent although major denticles can be identified in some parts of the 
bar. The anterior-lateral process is short, vertically depressed, slightly laterally 
deflected, and bears 1 to 4 denticles anterior to the main denticle, with the whole of 
the antero-lateral face undenticulated, and a more or less sharp convex edge. 

In lateral view the aboral surface of the unit is straight to gently concave. Its 
outer face is flat to steeply convex in the anterior part, but becomes more strongly 
convex in the medial and posterior part. The main denticle is not conspicuously 
larger than those which lie behind it. The denticles of the main part of the posterior 
bar are crowded and fused for most of their length, being slightly inclined posteriorly 
and tending to increase slightly in size towards the mid-point of the unit in some 
specimens. In other specimens the main denticle is up to twice as large as the main 
denticles of the posterior series, and in the latter, the hindeodellid character is more 
or less conspicuously developed. The inner lateral face of the unit is flat to gently 
convex. 

The antero-lateral process makes an angle of about 90 ° with the posterior bar. Its 
postero-aboral edge is straight and points vertically, and makes an antero-aboral 
angle at the anterior edge of about 45 °. The denticles anterior to the main denticle 
tend to be about equal in height to those of the major denticles of the posterior bar, 
and curve upwards to lie more or less parallel to the main denticle. The lowermost 
anterior edge of the antero-lateral process is undenticulate. 

The posterior bar is strongly laterally compressed. Beneath the main denticle 
there is a cavity which flares slightly at the edges, and this is extended posteriorly, 
and to a less extent, anteriorly as a narrowing groove. 

Hindeodella corpulenta Branson & Mehl 
Plate 29, figs. i6a-i7c 

1934 Hindeodella sp. Branson & Mehl : PI. 14, fig. 15. 

1934 Hindeodella corpulenta Branson & Mehl : 281, PI. 22, figs. 32, 33. 

1934 Metaprioniodus fr actus Huddle : 58, PL 11, figs. 14, 15. 

1934 Ligonodina conidens Huddle : 63, PI. 12, figs. 18, 19. 

1938 Ligonodina angulata Branson & Mehl : 142, PL 34, fig. 43. 

1939 Ligonodina conidens Huddle ; Cooper : 390, PL 45, fig. 45. 



BRITISH AVONIAN CONODONT FAUNAS 121 

1944 Ligonodina angulata Branson & Mehl ; E. B. Branson : PL 39, fig. 43. 

1947 Hindeodella millerella ? Youngquist & Peterson : 245, PI. 38, figs. 1-5. 

1949 Hindeodella cf. Hindeodella corpulenta Branson & Mehl ; Thomas : 408, PI. 1, fig. 4. 

1957 Hindeodella ? sp. Lys, Serre & Deroo : 800, PI. 9, fig. 1. 

Material. 168 specimens : figured, X 160, X 161. 
Range. North Crop KL i-ZLA 33, Avon Gorge K 2-Z 37. 

Description. The main denticle is massive with a sub-circular cross-section at 
the oral extremity. It is ovate at its base, feebly recurved and posteriorly inclined. 
It is about one and a half times as wide as the next largest denticle. The anterior 
lateral process is deflected laterally through 90 °, and depressed downward through 
90 °. It commonly bears 6 isolated, sub-circular denticles, which increase in size in 
the mid part. The posterior bar is massive, laterally compressed and bears about 5 
massive, discrete, feebly laterally compressed, posteriorly inclined denticles, the 
largest being in the posterior third. No smaller " hindeodellid " denticles are 
present. The posterior bar is deflected downward slightly towards the posterior end. 

In aboral view the large cavity is situated just anterior to the main denticle, and 
extends beneath the anterior lateral process. It is grooved along its mid-length. 
The inner lateral face may bear a feeble longitudinal ridge. 

Remarks. Most specimens of this species have the posterior bar broken, but the 
distinctive anterior lateral process and the basal cavity serve to identify it. 



Hindeodella croka Collinson & Druce 

Plate 28, figs. 15-17 

1957 Hindeodella brevis Branson & Mehl ; Bischoff : 26, PL 6, fig. 24. 
1961 Hindeodella brevis Branson & Mehl ; Higgins : PL 10, fig. 14. 
Hindeodella croka Collinson & Druce in press. 

Material. 7 specimens : figured, X 164, X 162, X 163. 

Range. North Crop 3D 9-3D 14/15. 

Description. The distinctive elongate form and enormously flexed anterior 
lateral process of the species are very distinctive features, and agree in all respects 
with the description of Collinson & Druce. There is a tendency in some specimens 
for the posterior bar to develop broadly hindeodellid denticulation, but this is not 
very clearly defined. In some specimens the anterior lateral process bears up to 8 
denticles. 

Remarks. A single specimen (PI. 28, fig. 29) is compared with this species, 
differing from it in the very strong lateral extension of the inner lateral face of the 
unit. It is extended laterally along the whole length of the unit posterior to the 
origin of the anterior lateral process, forming a platform-type flange, with a rather 
flat, oral surface and a convex to vertical outer lateral face. The relatively incon- 
spicuous main denticle is strongly inflexed, downflexed and less strongly recurved. 



122 BRITISH AVONIAN CONODONT FAUNAS 

Hindeodella hibbardi Collinson & Druce 
Plate 28, figs. 18-20 

1957 Angulodus walrathi (Hibbard) Bischoff : 17, PI. 5, figs. 44, 45. 
1961 Angulodus walrathi (Hibbard) Higgins PI. 10, fig. 16. 
Hindeodella hibbardi Collinson & Druce in press. 

Material. 22 specimens : figured, X 167, X 168, X 169. 
Range. North Crop 3D 11-3D 14/15. 

Description. This species of Hindeodella is characterized by a relatively long 
anterior lateral process, which is one third to one quarter the length of the posterior 
bar, and which is depressed and deflected at the bottom. Immediately anterior to 
the main denticle the anterior lateral process is depressed at an angle of about 110° 
to the posterior bar. Then, at a distance of about one quarter of its total length from 
the main denticle, it is inflexed by lateral twisting, so that the denticles anterior to 
this point of inflection point both inwards and also are curved upwards. At a further 
point about two-thirds of its length from the main denticle, it is again depressed in a 
vertical plane, and the remaining 3 distal denticles of the anterior lateral process are 
larger and more strongly recurved than those behind them. The oral surface of the 
anterior lateral process bears up to 10 stout denticles, more or less sub-circular in 
cross-section, discrete, tending to increase in size distally from the main denticle, 
although the most anterior is smaller than those immediately behind it. The 
process becomes thinner towards the anterior end, the antero-aboral extremity being 
bluntly rounded or plough-like in general form. The proximal end of the anterior 
lateral process and virtually the whole length of the posterior bar have conspicuously 
and strongly convex lateral faces. The denticles of the posterior bar are strongly 
developed, and curve inward, being inclined posteriorly at an angle of about 45°. 
The denticles of the main series are each separated by up to 4 smaller, fused, crowded 
denticles, which are less than half the length and diameter of those of the larger 
series. The posterior third of the unit is slightly depressed vertically and is deflected 
laterally. 

A very conspicuous aboral groove runs the whole length of the unit, being wide but 
rather shallow, and having conspicuous lateral lips. It is reduced in width towards 
the anterior and posterior end, and is widest below the main denticle where it is 
marked by a more or less conspicuous biconvex pit, both ends of which are relatively 
pinched in relation to the rest of the cavity. The outer lateral face is rather less 
convex than the inner. 

The main denticle is relatively small and inconspicuous in comparison with other 
denticles of the series. The whole unit is elongate, but in some specimens the lateral 
faces tend to be less convex than others, giving the whole unit a more slender 
appearance. In complete specimens the aboral cavity is seen to extend only for 
about half the length of the posterior bar. 



BRITISH AVONIAN CONODONT FAUNAS 123 

Hindeodella ibergensis Bischoff 

Plate 28, figs. 22-24, 3°> 3 1 

1957 Hindeodella ibergensis Bischoff : 28, PI. 8, figs. 33, 37, 39. 

1957 Hindeodella ibergensis Bischoff ; Ziegler in Fliigel & Ziegler : 42, PI. 5, figs. 14, 21. 

1957 Hindeodella germana Holmes ; Ziegler in Fliigel & Ziegler : 41, PI. 5, fig. 16. 

1958 Hindeodella redunca Stanley : 466, PI. 63, figs. 1-4. 

1961 Hindeodella ibergensis Bischoff ; Higgins : PI. 10, fig. 15. 

1962 Hindeodella ibergensis Bischoff ; Higgins : PI. 1, fig. 11. 

1963 Hindeodella ibergensis Bischoff ; Bouckaert & Higgins : 17, fig. 3. 
Hindeodella ibergensis Bischoff ; Collinson & Druce in press. 

Material. 37 specimens : figured, X 170, X 171, X 172, X 173, X 174. 

Range. North Crop 3D 10-3D 19. 

Description. This species includes greatly elongate hindeodellids, with the oral 
edge crowded with a series of alternating denticles. The aboral edge is straight to 
sinuous. In complete specimens the posterior bar decreases in width progressively 
towards the more or less pointed posterior tip. The main denticle is distinct, 
incurved and posteriorly deflected through 45 °, being about twice the diameter of the 
largest denticles of the main posterior series. The antero-lateral process is short, its 
total length being only about one eighth to one tenth that of the posterior bar. Its 
postero-aboral edge makes an angle of approximately 90 ° with that of the posterior 
bar immediately adjacent to it. Its anterior inner edge is flexed slightly inwards and 
there is a series of 3 or 4 recurved, inwardly inclined denticles, which are more or less 
discrete pointed, and decrease in size towards the distal end, which is sharply pointed. 
Both the degree of " hindeodellid " alternation of the denticles of the posterior bar 
and the posterior inclination of the denticles show considerable variation, as also 
does the degree of convexity of the lateral faces of the posterior bar, which tends to 
increase posteriorly. All denticles of the posterior bar are either very closely spaced 
or fused for most of their length, the 3 or 4 which form the posterior end lying almost 
horizontally. 

Remarks. The only substantial difference between this species and H. cooperi is 
the distinctive denticulation of the anterior lateral process, which in the present 
species extends as far as the aboral tip of the bar, in contrast to H. cooperi where it is 
restricted to the proximal part. 

Hindeodella montanaensis (Scott) 
Plate 28, figs. 21, 26 

1942 Lochreia montanaensis Scott {partim) : PI. 39, fig. 7, PI. 40, fig. 18 (non pi. 39, figs, i, 

4, 9 ; PI. 40, figs. 2, 9, 10, 12, 13, 15, 19). 
1956 Hindeodella bigeniculata Elias [partim) : 106, PI. 1, figs. 20, 21 {non PI. 1, fig. 16). 

1956 Hindeodella mehli Elias : 108, PI. 1, figs. 22-24. 

1957 Hindeodella germana Holmes ; Bischoff {partim) : 27, PI. 6, fig. 32, {non PI. 6, fig. 34 = 
H. secarata Collinson & Druce). 

1958 Hindeodella montanaensis (Scott) Stanley {partim) : 465, PI. 64, figs. 1-5. 



i2 4 BRITISH AVONIAN CONODONT FAUNAS 

1961 Hindeodella germana Holmes ; Higgins (partim) : PI. 10, fig. 12, (non PI. 10, fig. 13 = //. 
secarata Collinson & Druce). 
Hindeodella montanaensis (Scott) ; Collinson & Druce in press. 

Material. 80 specimens : figured, X 175, X 176. 

Range, North Crop 3D 10-3D 19. 

Description. Members of this species are slightly constructed hindeodellids, 
having a massive main denticle with a very wide base, strongly convex lateral faces, 
and being inclined posteriorly at an angle of about 45 °. The denticles on the 
posterior bar are minute in comparison with this denticle. They are crowded and 
laterally compressed, with sharp anterior and posterior edges, having a hindeodellid 
pattern with 2 or 3 smaller denticles between the larger ones. The lateral faces of 
the posterior bar are gently to strongly convex. The anterior lateral process is deep 
with three confluent denticles near its proximal end, but the distal end, which points 
strongly upward and inward, consists of a single fang-like denticle, about half the 
width of the main denticle. The basal anterior and posterior edges of the main 
denticle are also minutely denticulate. The outer lateral surface of the main denticle 
is flat. The aboral surface of the whole unit is excavated by a shallow groove which 
flares below the main denticle. The posterior bar is straight and about 5 to 6 times 
the length of the anterior bar in the present specimens, but these are broken. One 
specimen, which is also broken, shows a tendency for the denticles near the posterior 
end of the bar to be relatively larger, about twice as large as most of the denticles of 
the posterior bar, although the aboral cavity is little expanded below the main 
denticle. 



Hindeodella secarata Collinson & Druce 
Plate 29, figs, n, 13-15 

1957 Hindeodella germana Holmes ; Bischoff (partim) : 27, PI. 6, fig. 34 (non PI. 6, fig. 32==//. 

montanaensis) . 
1961 Hindeodella germana Holmes ; Higgins (partim) : PI. 10, fig. 13 (non PI. 10, fig. 12 = //. 

montanaensis) . 
1963 Hindeodella germana Bischoff ; Bouckaert & Higgins ; 17, fig. 3. 

Hindeodella secarata Collinson & Druce in press. 

Material. 46 specimens : figured, X 184, X 181, X 182, X 183. 

Range. North Crop 3D 8-3D 19. 

Description. The present specimens agree closely with the description given by 
Collinson and Druce. The posterior bar is greatly elongated and tends to taper 
towards the posterior end. It is straight to arched, with fine acicular denticles, and 
it lacks a well-developed anterior fang. The anterior process is very small, and is 
relatively feebly inflexed. The basal groove is conspicuous, but there is no obvious 
basal cavity at the anterior end. 



BRITISH AVONIAN CONODONT FAUNAS 125 

Hindeodella subtilis Ulrich & Bassler 
Plate 29, figs. 6a-7b, 9-iob 

1926 Hindeodella subtilis Ulrich & Bassler : 39, PI. 8, figs. 17-19. 

1927 Hindeodella deflecta Hibbard : 207, fig. 40. 

? 1928 Hindeodella germana Holmes : 25, PI. 9, fig. 9. 

1928 Hindeodella subtilis Ulrich & Bassler ; PI. 9, figs. 10, 11. 

1931 Hindeodella subtilis Ulrich & Bassler ; Cooper : 147, PL 20, fig. 9. 
? 1931 Hindeodella pumilla Cooper : 236, PI. 28, fig. 18. 

? 1931 Hindeodella subtilita Cooper : 236, PI. 28, fig. 17. 

1932 Hindeodella subtilis Ulrich & Bassler ; Bassler : PI. 26, fig. 21. 
1934 Hindeodella delicatula Branson & Mehl : 280, PI. 22, fig. 30. 

1934 Hindeodella alternidens Huddle : 44, PI. 5, fig. 13 (non PI. 5, fig. 12 — Hindeodella sp.). 

1934 Hindeodella angulus Huddle : 44, PI. 5, fig. 15. 

1934 Hindeodella aculeata Huddle : 40, PI. 4, fig. 19 (non PI. 4, figs. 20, 21= Hindeodella 
sp. cf. H, similis Ulrich & Bassler), PI. 5, figs. 2, 3. 

1934 Hindeodella grandis Huddle : 41, PI. 4, fig. 22. 

? 1934 Hindeodella laticlavis Huddle : 43, PI. 5, figs. 9, 10. 

1935 Hindeodella subtilis Ulrich & Bassler ; Cooper : 309, 310, PI. 27, fig. 27. 
1935 Hindeodella germana Holmes ; Cooper : 310, PI. 27, fig. 25. 

? 1935 Hindeodella pumilla Cooper ; Cooper : 310, PI. 27, fig. 26. 

? 1935 Hindeodella subtilita Cooper ; Cooper : 310, PI. 27, fig. 28. 

1938 Hindeodella delicatula Branson & Mehl ; Branson & Mehl, PI. 33, fig. 34. 
? 1939 Hindeodella lineata (Pander) Cooper : 389, PI. 46, figs. 28, 31. 

1939 Hindeodella delicatula ? Branson & Mehl ; Cooper : 389, PL 46, fig. 33. 

1939 Hindeodella acuta Branson & Mehl ; Cooper : 389, PL 46, figs. 15, 23, 29. 

1940 Hindeodella moweri Stauffer : 424, PL 58, figs. 2, 10, 11. 

1943 Hindeodella subtilis Ulrich & Bassler ; Cooper & Sloss : 170, PL 28, figs. 22, 32, 33. 

1943 Hindeodella atteridens Huddle ; Cooper & Sloss : 170, PL 28, fig. 23. 

1943 Hindeodella petila Cooper ; Cooper & Sloss : 170, PL 28, figs. 26, 35. 

1943 Hindeodella deflecta Hibbard ; Cooper & Sloss : 170, PL 28, figs. 27, 34. 

1943 Hindeodella germana Holmes ; Cooper & Sloss : 170, PL 28, fig. 28. 

1943 Hindeodella grandis Huddle ; Cooper & Sloss : 170, PL 28, figs. 31, 37, 39. 

1943 Hindeodella laticlavis Huddle ; Cooper & Sloss : 170, PL 28, fig. 38. 

1945 Hindeodella aculeata Huddle ; Cooper : 613, PL 84, figs. 7, 9. 

1945 Hindeodella rotunda Hibbard ; Cooper : 614, PL 84, fig. 8. 

1945 Hindeodella grandis Huddle ; Cooper : 614, PL 84, fig. 10. 

1945 Hindeodella gracilis Huddle ; Cooper : 614, PL 84, fig. 11. 

1945 Hindeodella prioniodon Huddle ; Cooper : 614, PL 84, fig. 12. 

1945 Metaprioniodus biangulatus Huddle ; Cooper : 614, PL 84, figs. 13, 14. 

1947 Hindeodella aculeata ? Huddle ; Youngquist & Petersen : 244, PL 38, fig. 9. 

1947 Hindeodella aculeata Huddle ; Bond : 28, PL 1, figs. 19, 21. 

1947 Hindeodella alternata Ulrich & Bassler ; Bond : 29, PL 1, fig. 23. 

1947 Hindeodella germana Holmes ; Bond : 29, PL 1, fig. 22. 

1947 Hindeodella germana Holmes ; Bond : 29, PL 1, fig. 22. 

1947 Hindeodella subtilis Ulrich & Bassler ; Bond : 29, PL 1, fig. 25. 

1947 Hindeodella sp. 1 Bond : 29, PL 1, fig. 24. 

1947 Hindeodella sp. 2 Bond : 29, PL 1, fig. 20. 

x 955 Hindeodella germana Holmes ; Sannemann : 130, PL 2, fig. 45. 

1955 Hindeodella deflecta Hibbard ; Sannemann : 129, PL s, fig. 6, PL 5, fig. 8. 

1957 Hindeodella germana Holmes ; Lys, Serre & Deroo : 800, PL 8, fig. 7. 

1957 Hindeodella deflecta Hibbard ; Lys, Serre & Deroo : 800, PL 8, fig. 6. 



126 BRITISH AVONIAN CONODONT FAUNAS 

1959 Hindeodella deflecta Hibbard ; Helms : PL 4, fig. 32, PI. 1, fig. 17. 

i960 Hindeodella germana Holmes ; Zimmermann : PI. i, fig. 16. 

i960 Hindeodella germana Holmes ; Dvorak & Freyer : PI. 1, fig. 1. 

1961 Hindeodella germana Holmes ; Budurov : 262, PI. 3, fig. 11. 

1962 Hindeodella germana Holmes ; Spasov & Stevanovic : 58, PI. 1, fig. 12. 
1962 Hindeodella sp. Winder : 91, fig. 1, 6. 

1965 Hindeodella germana Holmes ; Spasov : 86, 87, PI. 1, fig. 10. 
1965 Hindeodella similis Ulrich & Bassler ; Spasov : 87, PI. i, fig. 11. 

Material. 200 specimens : figured, X 180, X 177, X 178, X 179. 
Range. North Crop KL i-ZL 19, Avon Gorge K 3-Z 38. 

Description. The main denticle is fairly massive, laterally compressed, biconvex 
in cross-section, recurved and posteriorly inclined. The anterior lateral process is 
curved inwards at an angle ranging from just a few degrees to nearly 90 °. The 
considerably laterally compressed anterior lateral process is finely denticulate, often 
with the largest denticles at the anterior. The posterior bar is very thin, compara- 
tively deep, and somewhat arched in some specimens, bearing fine, discrete, pointed 
denticles. The dentition tends to be cyclic, two major denticles being separated by 
three to four minute denticles, all more or less posteriorly inclined. There are up to 
14 major denticles on the posterior bar. The posterior termination is composed of 
flat lying denticles, inclined at a low angle to the horizontal. It may be aborally 
convex (" upswept ") in young forms. 

The basal cavity is small, fairly deep, and situated at the anterior end of the apical 
denticle. 

Remarks. Throughout the Middle and Upper Devonian, and the Tournaisian and 
Visean, there occurs a simple hindeodellid with a curved anterior lateral process. 
Many different authors have assigned different names to these hindeodellids, depend- 
ing on minor variations in such features as the amount of deflection. Within our 
collections all types of deflection and various types of dentition can be seen to inter- 
grade, and it is probable that all these forms belong to the same variable species. 
Further work may show that some of these characteristics may be of specific import- 
ance, but at the present time none can be separated. 

Hindeodella tenuis Clarke 
Plate 28, fig. 27 

1900 Ctenognathus obliquus Hinde (partim) : 344, PI. 10, fig. 38. 
1928 Hindeodella obliqua Holmes (partim) : 12, PI. 5, fig. 5. 
i960 Hindeodella tenuis Clarke : 8, 9, PI. 1, figs. 10, 11. 

Material. 4 specimens : figured, X 187. 

Range. North Crop 3D 12-14/15. 

Description. The present specimens are similar to those described by Clarke. 
The posterior bar is elongated, deep, and decreases relatively little in depth towards 
its posterior end. The anterior two-thirds is straight and the posterior third gently 
down-flexed. The denticles tend to increase in size posteriorly, the most posterior 



BRITISH AVONIAN CONODONT FAUNAS 127 

being both the largest and the most steeply inclined. The anterior fang is two to 
three times the basal width of the largest of the posterior denticles, and is slightly 
recurved. The anterior bar is relatively short and the denticles stand erect. The 
larger denticles of the posterior bar are separated by only 1 or 2 smaller denticles. 
The anterior lateral process is not strongly inflexed. 

Hindeodella undata Branson & Mehl 

Plate 31, fig. 1 

1941 Hindeodella undata Branson & Mehl : 169, PI. 5, fig. 3. 

1941 Hindeodella sp. Branson & Mehl : 170, PI. 5, fig. 9. 

1953 Hindeodella undata Branson & Mehl ; Hass : 82, PI. 16, figs. 5-7. 

1956 Hindeodella undata Branson & Mehl ; Elias : 108, PI. 1, figs. 2, 10. 

1956 Hamulosodina bransoni Elias : 108, PI. 1, fig. 4. 

1956 Hamulosodina hassi Elias : 108, PI. 1, figs, n, 12. 

1 96 1 Hindeodella undata Branson & Mehl ; Higgins : PI. 12, figs, 10, 12. 

1963 Hindeodella undata Branson & Mehl ; Bouckaert & Higgins : 17, text-fig. 3. 
Hindeodella undata Branson & Mehl ; Collinson & Druce in press, text-fig. 10. 

Material. 35 specimens : figured, X 185. 

Range. North Crop 3D 4-3D 22. 

Description. Specimens of this species are characterized by a relatively long, 
deep and straight posterior bar, the aboral margin of which is straight and sharp, and 
the sides relatively flat. The oral surface bears a series of alternating denticles which 
are acicular in general form, and discrete for the whole of their length. They taper 
sharply to a point. Larger denticles tend to be separated by groups of 2 or 3 smaller 
ones, which may be laterally offset from the denticles of the main series. The 
anterior fang is not greatly larger than the largest of the denticles of the posterior 
bar. It makes almost a right angle with the line of the posterior bar and is straight 
for the greater part of its length. The anterior inner lateral process is short and 
continuously inflexed. It bears one or more needle-like denticles on its oral edge. 

Hindeodella sp. 
Plate 29, figs. 12a, c 

Material, i specimen : figured, X 445. 

Range. North Crop ZLA 33. 

Description. A single specimen of a small distinctive hindeodellid is illustrated. 
The posterior bar is short and relatively deep and bears a series of 5 denticles which 
increase in size posteriorly. The inclination of the 4 most posterior is about 45 ° to 
the line of the posterior bar, but the most posterior denticle is more strongly inclined. 
The apical denticle is rounded in cross-section and the lower part is more or less erect. 
The anterior process is sharply down-flexed and continuously inflexed, so that its 
distal end makes an angle of about 45 ° with the posterior bar. There is a well- 
developed, elongated basal cavity below the fang and the proximal part of the 
anterior aboral process. 



BRITISH AVONIAN CONODONT FAUNAS 



Hindeodella sp. nov. 
Plate 28, figs. 14a, b 



Material, i specimen : X 186 (figured). 

Type locality and horizon. North Crop. Sample 3D 14/15. 

Description. A single specimen is tentatively regarded as a new species of 
Hindeodella, although it may be a pathologic form. It is characterized by a con- 
tinuously recurved, hooked anterior lateral process and a very sinuous posterior bar. 
The general appearance of the unit is of a question mark, with the posterior end 
forming the base of the question mark. The posterior bar is shallow, being about 
equal in depth to the smaller series of denticles developed on its oral surface. Its 
aboral edge is strongly convex in its anterior half and concave in its posterior half, so 
that the whole effect is of a sinuous development. Its outer lateral face is strongly 
convex in the anterior half, and flat to gently convex in the posterior part. 

The oral surface of the posterior bar bears a series of about 18 denticles of variable 
size, which show no regular alternation. They are basally confluent but apically 
distinct, and are sharply pointed, with sharp anterior and posterior edges. Those 
near the posterior end tend to be more strongly inclined posteriorly than those in the 
anterior part, which are only gently inclined posteriorly. Although these denticles 
show no regular alternating arrangement, some of them are conspicuously larger than 
others and these are developed at variable intervals. The largest of them are about 
twice the length of the smallest, and they show a broad tendency to increase in size 
posteriorly. Their total number is probably greater than 18 as the present specimen 
is broken. The main denticle is about equal in size to the largest denticles of the 
posterior bar, being sharply recurved and incurved. Immediately posterior to it the 
aboral surface of the posterior bar is flat, although its general structure is still broadly 
convex. 

The antero-lateral process consists of two more or less distinct parts. There is a 
sharply up-flexed part, in which the aboral edge of the process makes an angle of 
about 70 ° with the aboral edge of the posterior bar immediately posterior to the main 
denticle. It is not greatly flexed to the natural plane, however. On the anterior end 
of this are two conspicuous denticles, which are incurved, as well as recurved, so that 
their " anterior and posterior " edges are in fact lateral in position. They are greater 
in size than the main denticle and exceed the size of the largest denticles of the 
posterior bar by about a half. The aboral surface of the unit is excavated by a very 
thin groove. 



Genus HINDEODUS Rexroad & Furnish 1964 

1964 Hindeodus Rexroad & Furnish : 671 
Type species. Trichonodella imperfecta Rexroad. 



BRITISH AVONIAN CONODONT FAUNAS 129 

Hindeodus alatoides (Rexroad & Burton) 
Plate 31, figs. 7, 10. 

1961 Falcodus ? alatoides Rexroad & Burton : 1152, PI. 140, fig. 8. 

1964 Hindeodus alatoides (Rexroad & Burton) Rexroad & Furnish : 67, PI. in, figs. 18, 19. 
1 96 1 Falcodus (?) n. sp. Rexroad & Collinson : PI. 1. 

1965 Hindeodus alatoides (Rexroad & Burton) Rexroad & Nicoll : 20, PI. 2, fig. 10. 

Material. 3 specimens : figured, X 193, X 192. 

Range. Scotland HOSIE 2B-2C. 

Description. The present specimens are distinguished by the short laterally 
flexed anterior limb, which is deepest and bears the largest denticles distally. The 
apical denticle is only slightly inclined posteriorly and its distal portion is straight. 
It is little compressed laterally. The posterior bar is straight and elongated, its 
length being about three times that of the anterior bar. The denticles are short, 
discrete and bluntly pointed, tending to alternate in size and standing more or less 
erect to the posterior bar in some specimens, but being slightly inclined in others. 
The apical denticle is conspicuously elongated, and has a basal width of up to three 
times that of the adjacent denticles. The denticles of the posterior bar tend to 
increase in size posteriorly. The aboral cavity is relatively small. 

Hindeodus imperfectus (Rexroad) 
Plate 31, fig. 8 

1957 Trichonodella imperfecta Rexroad : 41, PI. 4, figs. 4, 5. 

1958 Trichonodella imperfecta Rexroad ; Rexroad : 26, PI. 4, fig. 6. 
1961 Elsonella ? imperfecta (Rexroad) Rexroad & Collinson : 6. 

1961 Elsonella ? imperfecta (Rexroad) Rexroad & Burton : 1152, PI. 141, fig. 1. 

1964 Hindeodus imperfectus (Rexroad) Rexroad & Furnish : 672, PI. 111, figs. 13, 14. 

1965 Hindeodus imperfectus (Rexroad) Rexroad & Nicoll : 20, PI. 2, fig. 11. 

Material, i specimen : figured, X 194. 

Range. Scotland HOSIE 2B. 

Description. The present specimens are generally fragmentary, but they show 



Apical denticle 



Posterior 
Anterior bor 

aboral 
Outer lateral face margin Posterior bar 

Lateral view 

Fig. 25. Hindeodus sp. showing morphological terms used in the text. 




130 BRITISH AVONIAN CONODONT FAUNAS 

the general symmetry of this species, a feature that is so striking that it led Rexroad 
in his initialdescription to assign it to the genus Trichonodella. The denticles tend to 
increase in size towards the distal third of the bars, and the apical denticle tends to 
stand erect between the converging denticles of the anterior and posterior bars. 
There is a feeble basal flange below the apical denticle. 

Hindeodus sp. 

Plate 22, figs. I7a-20b 
1964 Hindeodus sp. Rexroad & Furnish : 672, PI. m, fig. 11. 

Material. 10 specimens : figured, X 189, X 191, X 188, X 190. 

Range. Scotland HOSIE 2A-2B. 

Description. Certain of the present specimens, although showing minor varia- 
tions in form, are obviously closely related to one another. These specimens possess 
a short, deep, posterior bar which has a straight aboral margin in lateral view. The 
bar is slightly flexed inwards longitudinally and its oral surface bears at least 10 
confluent denticles, only their apices being discrete and bluntly pointed. They are 
inclined gently posteriorly and are more or less of uniform size. The apical denticle 
is about twice as long as the largest denticles of the rest of the bar. It is basally 
confluent to those on either side of it and has sharp anterior and posterior edges and a 
strongly biconvex cross-section. The anterior bar is shorter than the posterior, and 
is gently concave basally in lateral view. Its oral surface bears a series of about 5 
denticles, similar in form to those of the posterior bar, which tend to decrease in size 
anteriorly and which are recurved so that they he sub-parallel to the apical denticle. 
It makes an angle of about 90°-iio° with the posterior bar. The denticles of the 
anterior bar tend on the whole to be rather broader than those of the posterior. The 
inner lateral face of the anterior bar is gently concave. In outer lateral view the 
whole unit is seen to be gently arched inwardly and its outer lateral face is flat to 
gently convex. There is a slightly expanded cavity below the apical denticle and 
very fine longitudinal grooves extend along the lengths of the two bars. 

Genus KLADOGNATHUS Rexroad 1958 

1958 Kladognathus Rexroad : 19 {pro Cladognathus Rexroad 1957, 28 non Burmeister 1847). 
1961 Cladognathodus Rexroad & Collinson : 6 (abs. syn.). 

Type species. Cladognathus prima Rexroad. 

This genus was first described by Rexroad in 1957 under the name Cladognathus, a 
name later found to be a homonym of one used by Burmeister in 1847. The name 
Kladognathus was proposed by Rexroad 1958, as a substitute. Rexroad & Collinson 
(1961 : 6), however, changed this to Cladognathodus because they suggested that the 
replacement of a letter " C " by a letter " K " did not represent a valid name change 
under the rules of nomenclature. Article 56A of the International Code makes it 
clear, however, that a difference of even one letter in the spelling of generic names 
represents a valid distinction between them. The name Kladognathus Rexroad 1958 



BRITISH AVONIAN CONODONT FAUNAS 131 

is thus the senior and correct name for the genus, and Cladognathodus Rexroad & 
Collinson 1961 is a junior synonym. We are grateful to Dr. Curt Teichert for 
pointing this out to us (see also Mound 1965). 

Kladognathus clarensis Collinson & Druce 
Plate 23, figs. ia-2b 
Kladognathus clarensis Collinson & Druce (in press). 

Material. 3 specimens : figured, X 195, X 196. 
Range. North Crop 3D 10-3D 23. 

Description. In lateral view this species resembles the genus Metalonchodina. 
Its most striking feature is the greatly enlarged, laterally compressed denticle which 
comprises most of the posterior bar. This is inclined posteriorly but the curvature 
may be more or less continuous, or it may be chiefly confined to the base, with the 
upper part of the denticle having straight anterior and posterior edges. The inner 
lateral face tends to be rather more convex than the outer. The posterior aboral 
termination is more or less sharply pointed. 

The fang is relatively small in comparison with the posterior denticle. It is 
slender, posteriorly continuously recurved, and has sharp anterior and posterior 
edges. The anterior bar consists of 1 to 3 denticles and the anterior aboral margin is 
spatulate in form with the anterior aboral angle being rounded. In multidenticulate 
anterior bars the most anterior denticles tend to be more or less erect, but the more 
posterior ones tend to be recurved. 

The lateral process is short and bears at least one oral denticle. The whole unit 
tends to be laterally deflected, the outer lateral face tending to be concave. The 
aboral surface below the main denticle on the posterior bar is broad, and has a 
conspicuous flattened basal surface. It consists essentially of an inverted basal 
cavity, with a median groove which is continued along the anterior bar. All of the 
three present specimens have a short, laterally compressed, inconspicuous denticle 
lying between the fang and the main denticle of the posterior bar. 

posterior 
Fong 



Anterior Bar /,/ Posterior denticle 




Aboral margin 
Fig. 26. Kladognathus sp. showing morphological terms used in the text. 



132 BRITISH AVONIAN CONODONT FAUNAS 

Remarks. The present specimens show strong resemblances to those described 
by Clarke (i960) as Ligonodina complectens. Rexroad & Collinson (1963 : 13) 
transferred Clarke's specimens to the genus Magnilaterella. The present specimens 
differ from those of Clarke chiefly in the presence of an anterior bar, and it is this 
distinctive feature which justifies their inclusion in the genus Kladognathus. 



Kladognathus macrodentatus (Higgins) 
Plate 23, figs. 3-6 

1961 Lambdagnathus macrodentata Higgins : 214, PI. 12, figs. 1-3, text-fig. 3. 

1963 Lambdagnathus macrodentata Higgins ; Bouckaert & Higgins : 17, fig. 3. 

Kladognathus macrodentata (Higgins) Collinson & Druce (in press). 

Material. 15 specimens : figured, X 197, X 198, X 199, X 200. 
Range. North Crop 3D 10-3D 22. 

Description. This species is characterized by a long arched posterior bar which 
bears characteristically hindeodellid denticulation on its oral surface. The larger 
denticles are separated by 1 or 2 smaller denticles, which are basally confluent but 
apically discrete. In well preserved specimens the major denticles of the series are 
very long, the largest, in the middle of the posterior blade, commonly being about 
three times the depth of the posterior bar. 

The short laterally compressed anterior bar is downflexed, but lies in the same 
plane as the posterior bar. Its anterior aboral margin is bluntly spatulate. There 
tend to be 2 or 3 small denticles in front of the apical denticle. The lateral bar is 
short, deeply arched, laterally compressed, and strongly deflected posteriorly, making 
an angle of 25°-45° with the arcuate posterior bar when seen in oral view. The 
lateral bar carries 1 or 2 stout, discrete denticles on its oral surface. The aboral 
margin of the entire unit is excavated by a shallow groove. 



Kladognathus mehli (Rexroad) 
Plate 31, fig. 15 

1957 Cladognathus mehli Rexroad : 29, PI. 1, figs. 11, 12. 

1958 Kladognathus mehli (Rexroad) Rexroad : 19, PI. 3, fig. 5. 

1965 Kladognathus mehli (Rexroad) Rexroad & Nicoll : 20, 21, PI. 1, fig. 7. 

Material. 3 specimens : figured, X524. 

Range. North Crop 3D 14/15. 

Description. This species is characterized by a very large, laterally compressed 
recurved fang, strong discrete denticles on the anterior and posterior bars, relatively 
strong curvature on the anterior and posterior bars, and a conspicuous attachment 
scar on the inner lateral face at the anterior end of the posterior bars. Our specimens 
agree closely with those illustrated by Rexroad. 



BRITISH AVONIAN CONODONT FAUNAS 



133 



Genus LIGONODINA Ulrich & Bassler 1926 

<,ssler : 218 (nom. nud.). 
rich & Bassler : 12, 13. 

Type species. Ligonodina pectinata Ulrich & Bassler 1926. 



1925 Ligonodina Bassler : 218 {nom. nud.). 

1926 Ligonodina Ulrich & Bassler : 12, 13. 



1934 
1934 
1934 
1939 
1943 
1944 

non 1944 

1947 

1949 

non 1949 

non 1964 



Ligonodina beata nom. nov. 

Plate 26, figs. 4~6b 

Ligonodina delicata Branson & Mehl : 199, PL 14, figs. 22, 23. 

Ligonodina delicata Branson & Mehl ; E. R. Branson : 328, PI. 27, fig. 3. 

Ligonodina sp. Huddle : 62, PI. 12, fig. 8. 

Ligonodina delicatula Cooper : 390, PI. 45, figs. 50, 60, 61. 

Ligonodina tenera Cooper & Sloss : 174, PI. 29, fig. 34. 



Ligonodina delicata Branson & Mehl 

PI. 93. fig- 74- 

Ligonodina delicata Branson & Mehl ; 

sp). 

Ligonodina delicata Branson & Mehl 

Ligonodina delicata Branson & Mehl 

Ligonodina delicata ? Branson & Mehl ; 

Ligonodina delicata Branson & Mehl ; 



Branson & Mehl in Shimer & Shrock : 



241, 



E. B. Branson : PL 26, fig. 23, (=Palmatolepis 



Miller & Youngquist : 509, 510, PL 73, fig. 12. 
Thomas : 408, 411, PL 4, fig. 22. 
Thomas : PL 3, fig. 41, (=Ligonodina sp.). 
Bergstrom : 28, text-fig. 12. Bergstrom 



non 1964 



(1964, 28) has demonstrated that Phragmodus delicatus Branson & Mehl, 1933, 123, 
PL 10, fig. 22) should be regarded as a species of Ligonodina. The name for this 
species, therefore, has precedence over that of Ligonodina delicata Branson & Mehl 
(1934, z 99) an< 3 the latter species becomes a junior homonym of the former. In 
this case, it is necessary to select a new name, and we have selected the name 
Ligonodina beata. The holotype is University of Missouri Catalogue No. C. 243-4 
(Branson & Mehl 1934 : z 99)- 
Ligonodina delicata Branson & Mehl ; Budurov & Tschurner : PL V, figs. 23a, b. 



Material. 361 specimens : figured, X 202, X 203, X 201. 
Range. North Crop KL 19-ZLA 21, Avon Gorge K 3-C 25. 

Description. A fragile unit with a slender main denticle which has a sub-circular 
cross-section. The main denticle is recurved posteriorly at 45 °. The anterior- 
aboral process originates immediately anterior to the main denticle, and commonly 
bears 3 or 4 isolated, discrete, sub-circular denticles, which are posteriorly inclined. 
The posterior bar is fairly long and rarely preserved. It bears up to 6 isolated 
laterally compressed denticles, which are posteriorly inclined, and tend to increase in 
size posteriorly. 

In aboral view, the anterior portion of the posterior bar is excavated, the deepest 
excavation being beneath the main denticle ; the cavity extends inverted beneath 
the anterior aboral process. The cavity is grooved, the groove running some way 
along the posterior bar and the complete length of the anterior aboral process. 



Remarks. 
& Mehl. 



Our specimens agree very closely to the holotype described by Branson 



134 BRITISH AVONIAN CONODONT FAUNAS 

Ligonodina levis Branson & Mehl 
Plate 26, figs. 15a, b, I7a-i9b 

1941 Ligonodina levis Branson & Mehl : 185, PI. 6, fig. 10. 

1949 Ligonodina sp. Youngquist & Miller (partim) : 620, PI. ioi, figs. 12 & 13 only. 

1957 Ligonodina levis Branson & Mehl ; Bischoff : 30, PI. 5, figs. 8, 9, PI. 6, fig. 25. 

1957 Ligonodina obunca Rexroad : 32, PI. 1, figs. 22, 23. 

1958 Ligonodina obunca Rexroad ; Rexroad : 21, PI. 3, figs. 7, 8. 

1961 Ligonodina levis Branson & Mehl ; Rexroad & Burton : 1154, PI. 141, figs. 7, 8. 

1963 Ligonodina levis Branson & Mehl ; Thompson & Goebel : 11, fig. 3. 

1963 Ligonodina levis Branson & Mehl ; Rexroad & Collinson : 11, PI. 2, figs. 24, 25. 

1964 Ligonodina levis Branson & Mehl ; Rexroad & Furnish : 672, PI. 111, fig. 381. 

1965 Ligonodina levis Branson & Mehl ; Rexroad & Nicoll : 21, PI. 2, fig. 24. 

Material. 25 specimens : figured, X 204, X 205, X 206, X 207. 
Range. North Crop CYD 6-3D 14/15, Avon Gorge Z 38-D 26. 

Description. Rexroad's original description of this particular species was rather 
generalized, but the distinctive features seem to be the massive and rather rounded 
main denticle, which is continuously recurved, especially in its lower part, so that its 
distal portion makes an angle of about 45 ° with the posterior bar. The distal 
portion is not greatly laterally compressed, although it has sharp anterior and 
posterior edges ; the lateral faces are themselves strongly convex. The posterior 
edges become obsolescent towards the proximal end. The outer lateral aboral 
surface is expanded slightly laterally, but has a conspicuous flange-like structure 
developed along it, which slopes towards the aboral cavity. The proximal inner 
portion of the main denticle is very strongly convex. 

The posterior bar is of unknown length but is more or less quadrate in cross-section, 
with a broad aboral edge. It bears at least one, stump-like denticle, which is well 
separated from the base of the main denticle. The antero-aboral surface of the main 
denticle tends to be rather rounded, and in oral-outer lateral view extends below the 
main level of the denticle in a rather bluntly pointed termination. The main 
denticle extends in a continuous curve downward to form the inner anterior aboral 
process. The aboral surface of this process lies at an acute angle, often as small as 
45 , to the posterior bar. Its oral surface bears up to 5 large denticles, of which 
those at the anterior end tend to be very large. They are straight to slightly curved 

Moin denticle 



Inner-loterol 
lamina 



Anterior aboral 
process 




Posterior denticles 



Posterior bar 



Fig. 27. Ligonodina sp. showing morphological terms used in the text. 



BRITISH AVONIAN CONODONT FAUNAS 135 

and are directed inwards and upwards. The denticles are discrete and more or less 
sub-circular in cross-section. 

The antero-aboral process decreases in thickness towards the distal end. The 
aboral surface is characterized by thick, aborally directed, lip-like, flange structures 
along the lateral edges of both the posterior bar and the antero-aboral process. 
There is a pit-like cavity below the main denticle and there are longitudinal grooves 
along the aboral surface of the posterior bar and the antero-aboral process. These 
decrease in width towards the distal end of the process. 

Ligonodina magnilaterina sp. nov. 
Plate 26, figs. 8a-nb 

Derivation of name. From the resemblance of the species to the genus Mag- 
nilaterella. 

Diagnosis. Ligonodinid with a denticle situated anterior to main denticle, 
forming continuation of denticle series of posterior bar. Anterior denticle only 
slightly smaller in size than main denticle, though tending to be rather more slender 
in general form ; lying at junction of antero-aboral process and posterior bar. 

Material. 6 specimens : Holotype X 211, Paratypes (all figured) X 208, X 209, 
X 210. 

Type locality and horizon. Scotland Sample HOSIE 2C. 

Range. Scotland HOSIE 2C. 

Description. The main denticle is strong, the base being strongly developed 
anteriorly and posteriorly. It is of unknown length, sub-circular in cross-section in 
the lower part. The main denticle is recurved in its lower part, the inner and outer 
lateral faces being strongly convex. The posterior margin of the main denticle is 
extended to form the oral surface of the posterior bar. This bar is of unknown 
length, but is deep in its anterior part and bears at least 4 discrete denticles, which 
are only slightly laterally compressed and of variable size. It is possible that they 
may be arranged in a cyclic pattern. 

On the anterior face of the main denticle a thickened denticle is developed at the 
junction of the anterior denticle and the antero-aboral process. This denticle is 
distinct from those of the antero-aboral process and in inner lateral view it seems to 
represent a continuation of the posterior bar. In outer lateral view it may be seen to 
be recurved inwardly at its base ; its anterior face is strongly convex with sharp 
lateral edges. It is recurved slightly posteriorly to lie sub-parallel to the main 
denticle, and also slightly inwardly. It is fused at the base to the main denticle and 
arises from it at a strongly convex junction. It is long and slender, being sharply 
pointed at its distal end and is about half the diameter of the main denticle. The 
other denticles of the anterior aboral process, which number at least three, are 
discrete, sub-circular in cross-section with poorly defined, but rather sharp, lateral 
edges. They tend to decrease in size distally. The anterior aboral process appears 
to be relatively short, although none of the present specimens is complete. It is 



136 BRITISH AVONIAN CONODONT FAUNAS 

strongly recurved in a vertical plane and its proximal aboral surface makes almost a 
right angle with the posterior bar. It is also strongly recurved with respect to the 
aboral surface of the posterior bar. The curvature of the anterior edge of the 
process is in line with the anterior denticle and not with that of the main denticle. 
It makes an angle of about 45 ° with the posterior bar in a horizontal plane. 

The aboral surface is excavated by a very shallow and rather inconspicuous 
groove, which runs along at least the anterior part of the posterior bar and is con- 
tinuous with a similar cavity below the anterior aboral process. The cavity below 
the main denticle is very narrow and not over-deep. 

Remarks. This species is distinguished from all other ligonodinids by the form 
and the position of the denticle anterior to the main denticle. In this feature it 
approaches, but does not reach, the typical forms of the genus Magnilaterella 
Rexroad and it is also reminiscent to some extent of some Ordovician species of the 
genus Phragmodus. 

Ligonodina osborni sp. nov. 
Plate 26, figs. ia-2c 

Derivation of name. This species is named in honour of Mr. S. Osborn of the 
Geology Department, University College of Swansea. 

Diagnosis. Ligonodinid with a conspicuous continuously recurved main denticle, 
strongly biconvex in cross-section, with feeble anterior and posterior edges, distal 
portion not preserved in present specimens. Posterior bar of unknown length, 
strongly depressed in vertical plane, bearing on oral surface series of isolated, 
posteriorly inclined denticles, appearing to increase in size posteriorly ; separated by 
distance about equal to their basal width. A short, sinuous, sharply flexed, pointed 
anterior aboral process, bearing 2 isolated denticles ; proximal larger than distal. 

Material. 6 specimens : Holotype X 212, Paratype X 213 (both figured). 

Type locality and horizon. North Crop. Sample 3D 14/15. 

Range. North Crop 3D 8-3D 14/15. 

Description. The main denticle is large and strongly recurved, its whole 
anterior edge being strongly convex, and its posterior strongly concave. The distal 
portion is of unknown form but the basal part is biconvex in outline, with only 
inconspicuously developed anterior and posterior edges. It is extended posteriorly 
into a strongly arched posterior bar, the aboral edge of which is concave. Its lateral 
faces are flat or only very feebly convex, and there is a sharp basal ledge developed 
along its preserved length. Its oral surface bears at least 3 isolated, posteriorly 
inclined, denticles, which are biconvex in cross-section, and the third of which is 
larger than the first or second. These are inclined at an angle of about 45 ° to the 
posterior bar, and are separated by a distance about equal to their basal width. 

The antero-aboral process makes an angle in a vertical plane of about 90 ° with the 
line of the posterior denticle, so that its denticles point directly inwards and also a 
little posteriorly, because of their recurvature. It bears at least 2 isolated denticles, 



BRITISH AVONIAN CONODONT FAUNAS 137 

which are biconvex in cross-section and have inconspicuous lateral edges. They are 
separated by a great distance and the distal is the smaller of the two. The whole 
anterior aboral surface tapers rapidly towards its distal tip ; although its depth 
remains constant, its width decreases conspicuously. Its distal tip is also flexed 
gently forward. In lateral view the most striking feature of the anterior aboral 
process is that it is so recurved posteriorly that it has an angular protruding junction 
with the base of the main denticle. It is then flexed forwards so that the whole 
appearance of the combined aboral process and anterior denticle is of a feebly sinuous 
line. In outer lateral view the flexure and decrease in width of the anterior aboral 
process are conspicuous features. The lip below the main denticle is also strikingly 
developed in lateral view, the whole inner lateral face of the unit being very feebly 
convex. In aboral view the unit is greatly expanded below the main denticle and 
there is a conspicuously flattened, but sloping, surface which is deeper on the outer 
lateral side. It narrows rapidly towards the posterior bar, which is excavated by a 
relatively deep, rounded groove. The main basal cavity is restricted to the median 
part below the main denticle. The anterior aboral process also has a very wide 
aboral surface, which is only partly excavated, but it narrows rapidly towards a 
pointed distal end and is somewhat twisted in aboral view. It is deflected to make 
an angle of 90 ° in a vertical plane with the main denticle. 

Ligonodina roundyi Hass 

Plate 26, figs. I3a-i4b, i6a-c 

1926 Prioniodus sp. A. Roundy : 11, PI. 4, fig. 9. 

1926 Prioniodus sp. C. Roundy : 11, PI. 4, fig. 11. 

1953 Ligonodina roundyi Hass : 82-83, PI. 15, figs. 5-9. 

1956 Ligonodina roundyi Hass : Elias: 126, PI. V, figs. 10-14. 

1958 Ligonodina roundyi Hass ; Rexroad : 21, PI. 3, figs. 1-4. 

1961 ^Ligonodina typa (Gunnell) Higgins : 220, PI. 11, fig. 6. 
Ligonodina roundyi Hass ; Collinson & Druce (in press). 

Material. 24 specimens : figured, X 214, X 215, X 216. 
Range. North Crop 3D 14/15. 

Description. This species of Ligonodina is characterized by a massive and 
elongate main denticle and a strongly developed antero-aboral process. The 
posterior bar is relatively slender in comparison with the proportions of the two 
latter elements. 

The main denticle is greatly elongated, and more or less strongly expanded 
anteriorly and posteriorly at its base. It is sharply pointed and in its distal half it is 
very strongly laterally compressed, the anterior and posterior edges being sharp and 
the lateral faces feebly convex. The curvature of the main denticle is concentrated 
in the proximal third, the remainder being straight. It is also twisted in the vertical 
plane, so that the anterior edge points inwardly ; in its outer aboral portion the main 
denticle is strongly rounded, but the corresponding inner lateral face is flat to feebly 
concave. Along the inner anterior margin a relatively strong and sharp keel is 



138 BRITISH AVONIAN CONODONT FAUNAS 

developed, which is the main anterior edge of the denticle ; it extends aborally as a 
sharp ridge, which forms the edges of the denticles of the anterior aboral process. 
The posterior face of the main denticle tends to become rather depressed and may 
develop a low concave depression. 

The antero-aboral process points vertically downwards, making an angle of 
8o°-ioo° with the posterior bar. It is not deflected out of line with the main denticle 
to any great extent. The oral surface of the anterior aboral process bears up to 6 
denticles, the largest of which occurs in the medial portion ; the denticles are 
strongly compressed anteriorly and posteriorly in their distal portions. Though 
their bases are sub-circular in outline, they have strong lateral edges and are recurved 
inward and upward ; they are discrete but relatively closely spaced. The posterior 
bar is relatively slender and bears at least 2 (the present specimens are all broken) 
discrete, sub-circular, widely spaced, feebly posteriorly inclined, bluntly pointed, 
peg-like denticles. 

The outer lateral face of the main denticle is strongly flared and the edges of the 
cavity are thick ; there is a deep, but limited lip below the main denticle which is 
extended along the aboral anterior process as a conspicuous longitudinal groove on 
the aboral surface ; it is also extended for at least some distance along the posterior 
bar. 

The width and depth on the antero-aboral process decrease towards the distal 
extremity, which is bluntly rounded. The posterior bar is more or less quadrate in 
cross-section. 

Ligonodina tenuis Branson & Mehl 
Plate 31, figs. 4, 16 

1941 Ligonodina tenuis Branson & Mehl : 170, PI. 5, figs. 13, 14. 

1949 Ligonodina sp. Youngquist & Miller (partim) : 620, PI. 101, fig. 11 only. 

1956 Ligonodina tenuis Branson & Mehl ; Elias : 126, PI. 5, figs. 4, 5. 

1957 Ligonodina sp. Rexroad : 33, PI. 1, figs. 20, 21. 

1957 Ligonodina hamata Rexroad : 32, PI. 1, figs. 24, 25. 

1958 Ligonodina hamata Rexroad ; Rexroad : 21, PI. 3, figs. 9-14. 
i960 Ligonodina tulensis (Pander) Clarke 11, PI. 2, fig. 4. 

1961 Ligonodina obunca Rexroad ; Higgins : PI. 11, fig. 9. 

1961 Ligonodina hamata Rexroad ; Rexroad & Burton : 1154, PI. 141, figs. 5, 6. 

1964 Ligonodina tenuis Branson & Mehl ; Rexroad & Furnish : 672, PI. in, fig. 40. 

1965 Ligonodina tenuis Branson & Mehl ; Rexroad & Nicoll : 22, PI. 2, figs. 12-15. 

Material. 15 specimens : figured, X 320, X 321. 

Range. North Crop 3D 8-3D 22. 

Description. Specimens of the species, though generally fragmentary, display 
the distinctive features of the holotype. They have a characteristically strongly 
developed long, slender main denticle, which is continuously recurved, although the 
distal portion tends to be rather straight : the lateral faces are convex to flat, and 
the aboral margin tends to bear a more or less conspicuous ledge. The denticles of 
the posterior bar are relatively small in comparison with the size of the unit. 



BRITISH AVONIAN CONODONT FAUNAS 139 

Ligonodina tulensis (Pander) 
Plate 31, fig. 9 

1856 Prioniodus tulensis Pander (partim) : 30, tab. 2a, fig. 19 only. 

1900 Prioniodus tulensis Pander ; Hinde (partim) : 343, PI. 9, fig. 15 only. 

1928 Prioniodus tulensis Pander ; Holmes (partim) : 22, PI. 3, fig. 22 only. 

Material. 6 specimens : figured X 328. 

Range. North Crop CYD 6-CYD 7. 

Description. The present specimens are fragmentary but they display most of 
the features described by Clarke. The main denticle tends to be rather large in 
comparison with the size of the posterior bar ; its lateral faces are flat to gently 
convex, and in its lower portion the anterior and posterior edges tend to be blunted. 
The denticles of the posterior bar are relatively small, and are discrete. The anterior 
aboral process is strongly recurved laterally, and is also twisted, so that the denticles 
are directed anteriorly. Its distal end makes a right angle in a horizontal plane with 
the posterior bar. The denticles of the process tend to be rather larger than those 
of the posterior bar. 

Ligonodina sp. A 

Plate 26, figs. 3a-c 

Material, io specimens : figured, X 217. 

Range. North Crop ZLA 32-ZLA 33. 

Description. All the present specimens are broken, but the species appears to be 
a ligonodinid with a greatly excavated main denticle. The main denticle itself is 
massive, sub-circular in cross-section, with a sharp lateral costa developed in line 
with the anterior aboral process. The antero-aboral process is broken, but the 
posterior bar can be seen to be short, bearing three tall isolated denticles, and having 
its aboral side grooved. 

Remarks. The overall appearance of this species is of a Roundya with only one 
limb of the anterior arch developed. Youngquist, Miller & Downs (1950 : 527) 
illustrate and describe similar forms as Ligonodina? sp. Our material is too frag- 
mentary for a specific designation but it would appear that the two forms may be 
conspecific. 

Ligonodina ? sp. 
Plate 26, fig. 7 

Material, i specimen : figured, X 218. 

Range. North Crop ZLA 11. 

Description. This appears to be a pathological form of L. beata. There is a 
secondary lateral process developed on the inner side of the posterior bar and it bears 
one low node. The angle of the process, and its inclination toward the posterior, are 
parallel to that of the antero-aboral process. The basal cavity is extended along it 
on the aboral side. 



M" BRITISH AVONIAN CONODONT FAUNAS 

Ligonodina ? sp. 
Plate 26, figs. I2a-b 

Material, i specimen : figured, X 219. 

Range. North Crop 3D 10. 

Description. This single specimen is presumably a pathological form of the 
genus Ligonodina. It is characterized by the presence of the antero-aboral process 
and by the fact that the main denticle can just be discerned when the lighting is 
favourable. On the posterior edge of this denticle, however, and continuous with it, 
there is a sheet-like development of conodont material which extends in the same 
plane as the posterior bar. Only the anterior denticle is visible within this by 
reflected light. The denticles of the antero-aboral process are sub-circular in form, 
3 in number, and discrete, the middle one of the three being the largest. The form 
of the outer lateral face of the extension of the anterior denticle suggests that the 
conodont was attached by this surface ; this then became an aboral surface although 
in " normal " specimens it would have represented an upper lateral surface. 



Genus LONCHODINA Ulrich & Bassler 1926 

assler : 219 (nom. nud.). 
lrich & Bassler : 

Type species. Lonchodina typicalis Ulrich & Bassler 1926. 



1925 Lonchodina Bassler : 219 (nom. nud 

1926 Lonchodina Ulrich & Bassler : 



Lonchodina bolbosa Collinson & Druce 

Plate 24, figs. I2a-i4b 

1957 Lonchodina nitela Huddle ; Ziegler in Fliigel & Ziegler : 44, PI. 4, fig. 19. 
1961 Lonchodina cf. projecta (Ulrich & Bassler) Higgins ; 220, PI. XI, fig. 10. 
Lonchodina bolbosa Collinson & Druce (in press). 

Material. 12 specimens : figured, X 223, X 222, X 224. 
Range. North Crop 3D 8-3D 14/15. 

Description. The distinctive features of this species are the relatively sub-equal 
short and rather slender bars, the conspicuous basal flaring below the apical denticle 
on the outer lateral face and the divergence of the two bars below the denticle at an 
angle of more than 90 ° ; in some specimens the angle approaches a right angle, but 
in others, the angle may be as high as no°. 

The present specimens are very fragmentary but they show the long recurved, 
laterally compressed apical denticle, the distinctive flaring cavity, and the straight 
and relatively short anterior aboral process described by Collinson & Druce. The 
basal excavation below the main denticle is large but shallow, and is extended as a 
very narrow groove along the anterior aboral process. 



BRITISH AVONIAN CONODONT FAUNAS 



141 



Lonchodina furnishi Rexroad 
Plate 24, figs. 2oa-23C 



1957 ? Lonchodina subsymmetrica Ulrich & Bassler ; Bischoff : PI. 1, figs. 19, 21, 22. 

1958 Lonchodina furnishi Rexroad : 22, PI. 4, figs. 11-13. 
1961 Lonchodina furnishi Rexroad 

non 1962 Lonchodina furnishi ? Rexroad 
1963 Lonchodina furnishi Rexroad 
Lonchodina furnishi Rexroad 



Higgins : PI. n, fig. 3. 
Higgins : PI. 1, fig. 4. 
Bouckaert & Higgins : 17, fig. 
Collinson & Druce (in press). 



3- 



Material. 5 specimens : figured, X 225, X 226, X 228, X 227. 

Range. North Crop 3D 8-3D 19. 

Description. The distinctive feature of this species is the more or less sym- 
metrical development of the cavity below the apical denticle on both sides of the bar, 
rather than being restricted to only one side of it. The anterior bar is stout and deep 
increasing slightly in depth towards the anterior end. It bears about 5 stout 
denticles which are basally confluent but discrete for two thirds of their length. 
They tend to be sub-triangular in profile and to be sharply pointed, with sharp 
anterior and posterior edges and gently to strongly convex lateral faces. The 
curvature on the outer faces tends to be stronger than that on the inner, the denticles 
on the median third of the bar tending to be the largest. The anterior denticle is 
small and relatively inconspicuous. The apical denticle is about twice the length of 
the largest denticle of the anterior bar ; it is strongly posteriorly inclined rather than 
recurved, its edges being straight. It lies in approximately the same horizontal plane 
as the distal end of the anterior bar. Its inner lateral face is strongly convex at the 
base, becoming feebly convex in its upper surface ; its outer lateral face is rather 
more strongly convex. Throughout its length it is sharply pointed and is also 
directed inwardly as well as posteriorly. The outer lateral face of the anterior bar is 
feebly ridged longitudinally along its upper surface, about one third of its depth below 
the junction with the oral denticles ; below this point it slopes gently inwards and 
has a flat feebly concave surface. The bar itself is curved in a vertical plane and is 
also slightly deflected inwardly. 



Posterior 



Posterior 
bar 



Apical denticle 




Aborai margin 



Anted op 



Anterior bor 



Inner lateral face 



Flared basal 
cavity 



Fig. 28. Lonchodina sp. showing morphological terms used in the text. 



i 4 2 BRITISH AVONIAN CONODONT FAUNAS 

The posterior bar is depressed, but is more or less straight ; it bears about 4 
denticles which are discrete, sub-triangular in profile and sharply pointed, their bases 
being confluent ; they have sharp posterior and anterior edges, feebly convex lateral 
faces, and are inclined parallel to the apical denticle, though they are not recurved 
inwardly to the same extent. The posterior bar is more shallow and slender than 
any part of the anterior bar and is only about one third to a half the length of the 
latter. 

Both bars are excavated by fine longitudinal grooves and there is a conspicuous 
flaring cavity below the apical denticle on both the inner and outer lateral faces of the 
unit, about which it is sub-symmetrical, though not symmetrical in detail, the inner 
lateral flaring occurring rather posterior to the outer lateral flaring. 

Remarks. The denticles on the anterior bar may number up to 8 in some 
specimens. The species shows some variation in the degree of lateral deflection of 
the bars in a horizontal plane. Some specimens (e.g. PI. 24, fig. 23b) show the 
posterior bar considerably flexed outward as well as vertically. 



Lonchodina obtunda Collinson & Druce 
Plate 24, figs. 7a-c 

1957 Lonchodina projecta (Ulrich & Bassler) Ziegler in Fliigel & Ziegler : 44, PI. 4, fig. 14 

(non PI. 5, fig. 12). 
1962 ? Lonchodina cf. projecta (Ulrich & Bassler) Higgins : PI. 1, fig. 5. 

Lonchodina obtunda Collinson & Druce (in press). 

Material. 5 specimens : figured, X 229. 
Range. North Crop 3D 8-3D 17. 

Description. The distinctive features of the species are the relatively delicate 
construction of the whole unit, the large sub-apical cavity which is developed on the 
inner lateral surface, and the very wide angle of divergence of the anterior and 
posterior bars, which in Collinson & Druce's type specimens is no "-135 °. 

The present specimens are incomplete but they show a relatively slender anterior 
bar, with about 5 widely spaced though virtually basally confluent, denticles ; they 
are curved upward and inward and have biconvex lateral faces, the inner being the 
stronger, and relatively sharp edges. The denticles of the anterior bar range up to 
at least 5 in number. The apical denticle is strong and more or less sub-circular in 
cross-section, though it has prominent anterior and posterior edges in its proximal 
portions ; it is curved inwards and backwards, and its inner lateral face is very 
strongly expanded to give a wide flaring basal cavity which extends as a groove along 
the bars. The posterior bar is broken in the present specimens but it makes an angle 
of considerably more than 90 ° with the anterior bar. 

Remarks. Collinson & Druce (in press) have discussed the relationships of 
this species with other lonchodinids. 



BRITISH AVONIAN CONODONT FAUNAS 143 

Lonchodina paraclarki Hass 
Plate 24, figs. 16a, b 

1953 Lonchodina paraclarki Hass : 83, PL 16, figs. 15, 16. 
non 1958 Lonchodina paraclarki Hass ; Stanley : 468, PI. 67, fig. 1. 
non 1958 Lonchodina cf. paraclarki Hass ; Rexroad : 22, PL 4, figs. 4, 5. 
Lonchodina paraclarki Hass ; Collinson & Druce (in press) . 

Material. 3 specimens : figured, X 231. 

Range. North Crop 3D 10-3D 14/15. 

Description. The most distinctive features are the very short posterior bar 
tending to develop only 2 denticles, the massive incurved and recurved apical 
denticle, and the very strong inner-lateral deflection of its aboral margin, giving a 
sub-triangular basal cavity that extends along most of the aboral surface of the unit. 
Hass has discussed the relationship of the species to Ligonodina clarki (1953 : 83) 
and Collinson & Druce have discussed the differences between Lonchodina paraclarki 
in the original sense of Hass and specimens referred to that species by Stanley & 
Rexroad. 

Lonchodina paraclaviger Rexroad 
Plate 24, figs. 15a, b, 18a, b 

1958 Lonchodina paraclaviger Rexroad : 22, PL 4, figs. 7-10. 

Lonchodina paraclaviger Rexroad ; Collinson & Druce (in press) . 

Material. 780 specimens : figured X 232, X 233. 

Range. North Crop 3D 13-3D 14/15. 

Description. This species is characterized by its stout general construction. 
The posterior bar is about half the length of the anterior bar. The stout, basally 
confluent, elongated, pointed denticles, number eight on the anterior bar, and four on 
the posterior. Both bars are straight except for slight curvature in the anterior, 
where they make an angle of about 90°-ioo° with each other. The lateral deflection 
of the posterior bar is about 45 ° out of the vertical plane of the anterior bar, and a 
large flaring asymmetrical cavity is strongly developed on the inner side, as a sub- 
triangular, to rounded expansion, that is flat on the outer lateral face and is extended 
along both bars as a deep groove. Both bars are relatively deep, with convex lateral 
faces. The denticles of the anterior bar, although basally confluent, are discrete for 
most of their length, and approach the apical denticle in size ; they may be of 
uniform size or they may increase in size towards the anterior end of the unit ; they 
are slightly recurved posteriorly and also inwardly, and lie more or less parallel to the 
apical denticle, which is sometimes only slightly larger than those of the anterior bar. 
The apical denticle is very strongly convex on its inner lateral face, with sharp 
anterior and posterior edges, and rather less strongly convex on its outer lateral face ; 
it is more or less straight in lateral view but is inclined posteriorly at about 60 ° to the 
anterior bar and is also recurved inwardly. The denticles of the posterior bar tend 



i 4 4 BRITISH AVONIAN CONODONT FAUNAS 

to be rather straight, but are discrete, sharply pointed, and tend to be directed 
inwardly, being either erect to the posterior bar or in a few cases sloping slightly 
forward ; in most specimens, however, they are either erect or posteriorly inclined. 
The posterior denticles tend to decrease in size posteriorly. 

The basal cavity is strongly developed on the inner side of the unit, but it is wide, 
rather than deep ; it extends as a very narrow groove along the bars. 

Lonchodina transitans Collinson & Druce 
Plate 31, fig. 14 
Lonchodina transitans Collinson & Druce (in press). 

Material. 3 specimens : figured, X 234. 

Range. North Crop 3D 4-3D 14/15. 

Description. The present specimens are incomplete but they show the essential 
features of the species, including the angle of divergence of the anterior and posterior 
bars of about 130 ° and the more or less bilaterally asymmetrical open " ligonodina " 
type cavity which is developed below the apical denticle. The apical denticle is 
recurved and relatively slender. The posterior bar is broken in the present speci- 
mens but bears at least 2 discrete, sharply pointed, posteriorly inclined denticles. The 
anterior bar is straight, and is slightly inflexed, as well as being depressed ; it bears 
at least 3 laterally compressed, recurved, slightly incurved denticles. Both bars are 
excavated by aboral grooves which extend into the shallow and rather flared cavity 
below the basal surface of the apical denticle. The apical denticle is biconvex in 
cross-section in its proximal part, and its strong lateral expansion on the outer face 
develops a suggestion of a median ridge on the lower part of that surface. 

Remarks. Collinson & Druce have pointed out that this species represents a 
transitional form between the genera Ligonodina and Lonchodina. 

Lonchodina sp. A 
Plate 24, figs. 17a, b 

Material. 6 specimens : figured, X 424. 

Range. North Crop ZLA 32-ZLA 33. 

Description. All the present specimens are broken, but they appear to represent 
a short unit, the bars being restricted. The apical denticle is large, laterally com- 
pressed and inclined toward the inner side. The bars appear to be curved on the 
outer side. The basal cavity is large and occurs beneath the apical denticle. 

Genus MAGNILATERELLA Rexroad & Collinson 1963 
1963 Magnilaterella Rexroad & Collinson : n. 
Type species. Magnilaterella robusta Rexroad & Collinson 1963. 



BRITISH AVONIAN CONODONT FAUNAS 145 

Magnilaterella complect ens (Clarke) 
Plate 23, figs. I4a-i7c 

1900 Prioniodus tulensis Hinde (partim) : 343, PI. 9, fig. 16. 

1928 Prioniodus tulensis Hinde ; Holmes (partim) : 22, PI. 3, fig. 20. 

i960 Ligonodina complectens Clarke : 9, PI. 1, figs. 14, 15. 

Material. 14 specimens : figured, X 240, X 237, X 238, X 239. 
Range. Scotland HOSIE 2A-HOSIE 2B. 

Description. This species is clearly a member of the genus Magnilaterella 
Rexroad & Collinson, but is not typical of that genus. The generic features are seen 
in the present specimens in the short form, strong inner lateral callus and basal 
groove of the lateral bar, and the deflected and upflexed general form of the posterior 
bar, the largest denticles of which are situated at the proximal end and which are 
strongly developed and strongly recurved and incurved. In contrast to other 
described forms of the genus Magnilaterella, however, the largest denticles of the 
lateral bar are situated at the anterior, and not at the posterior end. This form, 
therefore, seems to approach Ligonodina, to which Magnilaterella is closely related. 
Rexroad & Collinson (1963 : 13) have discussed the relationships between the two 
genera, but the character of the present specimen alters the view of the distinctive 
nature of the denticulation of the posterior bar. 

The lateral bar is short and in inner view is deep ; the most anterior denticle is 
enormously developed and strongly recurved in its lower portion, its distal half being 
more or less straight, although the distal posterior edge is so sharply pointed that it 
gives it almost a sigmoidal appearance. The two remaining denticles of the posterior 
bar are inconspicuous by comparison with the major denticle ; they are isolated, 
small, sub-circular, and more or less sharply pointed. The posterior bar is curved 
sharply backward and upward and the proximal denticle is very strongly developed. 
It approaches, but does not quite equal, the major denticle in size ; it is biconvex in 
cross-section, with bluntly developed anterior and posterior ridges in its upper half, 
but in the proximal half it is convex on the anterior face and has a concave posterior 
depression on its posterior edge. The inner lateral face is strongly convex and it 
bears at least one small isolated sub-circular denticle. The largest denticle of the 
posterior bar is recurved and deflected parallel to the major denticle. 

The aboral surface of the unit is conspicuously grooved ; the outer aboral surface 
tends to be flat and rather extended below the major denticle, but the inner aboral 
surface is strongly developed as a callus, which runs up the inner face of the lateral 
bar. This slopes down to give a relatively narrow, horizontal, aboral surface, 
parallel to the base of the groove. In more complete specimens the lateral bar is seen 
to taper to a point at its distal end ; it may bear only 2 denticles including the most 
anterior denticle. In more complete specimens the posterior bar may bear up to 6 
denticles in specimens which tend to decrease distally in size ; when viewed orally it 
makes an angle of about 30 ° with the lateral bar. In the specimen shown in PI. 23, 
fig. 14 a small and relatively inconspicuous denticle is developed in front of the largest 



146 BRITISH AVONIAN CONODONT FAUNAS 

denticle of the lateral bar, being about equal in height to the larger denticles of the 
posterior bar. 

When viewed aborally the most striking feature of this species is the broad 
extension of the aboral surface, represented by the flange, and the restriction of the 
warped and flexed sinuous cavity to the outer lateral margin of the scar, which the 
flange forms. 

Magnilaterella clarkei sp. nov. 
Plate 23, figs. n-i3b 

1900 Polygnathus convexus Hinde [partim) : 342, PI. 9, fig. 7. 

1928 Lonchodus convexus (Hinde) Holmes (partim) : 14, PI. 6, fig. 14. 

i960 " Gen. et sp. nov? " Clarke : 16, PI. 11, figs. 10, 12, 13. 

Derivation of name. After Dr. W. J. Clarke. 

Diagnosis. Magnilaterella characterized by massive development of strongly 
depressed, continuously curved posterior bar, gently flexed inward in its median part, 
its denticles tending to be largest in its mid-third. Denticles of lateral bar large, 
sub-triangular, separated by smaller single denticles. Posterior bar of insignificant 
size in comparison with lateral bar, but strongly inflexed. 

Material. 23 specimens : Holotype X 431, Paratypes X 241, X 432 (all 
figured). 

Range. Scotland DUN 52-80, GILM 3-BIL 102. 

Description. This is a rather typical species of the genus Magnilaterella, with a 
very elongated and very deep posterior bar, which becomes deeper in its posterior 
part. It has a very feebly convex inner-lateral face and is bowed slightly out- 
wards along its length. It is continually recurved with a conspicuous concave aboral 
surface. The oral surface bears up to 4 main denticles, which tend to be largest in 
the median third and decrease in size in both directions. They are conspicuously 
triangular in lateral view and are sharply pointed. The denticles have very sharp 

inner lateral face 




Lateral bar 



Basol groove 
Fig. 29. Magnilaterella sp. showing morphological terms used in the text. 



BRITISH AVONIAN CONODONT FAUNAS 147 

anterior and posterior edges and feebly convex to flat lateral faces. They are 
separated by a single similar denticle, widely spaced between them but only about 
one fifth to one sixth of the length of the larger denticles they separate. The 
posterior end of the lateral bar is marked by one such denticle which extends 
downwards to form the bluntly triangular distal end of the bar. At the anterior end 
of the lateral bar there are 2 to 3 smaller denticles of this general kind. The inner 
aboral surface of the posterior bar is marked by a variably developed flange, which 
although laterally persistent is irregular in the extent to which it invades the lateral 
face of the unit. It tends to do this to a rather small degree and its greatest aboral 
extension is under the posterior third of the bar. 

The posterior bar is very small in comparison with the lateral bar and is strongly 
recurved, so that in oral view it makes an angle of about 30 ° with the lateral bar. It 
is also sharply convex and seems to bear rather small denticles although in the present 
specimens it is broken. The largest of these small denticles, occurs at its junction 
with the lateral bar. It tends to decrease in depth distally at its junction with the 
lateral bar, just anterior to the bluntly spatulate termination of the latter. In outer 
lateral view the outer lateral bar is flat and the outer lateral surface of the denticles 
are also markedly flat ; only a few of them show any degree of convexity. There is no 
sign in outer lateral view of the scar-like presence of the inner callus. In aboral view 
a thin slit occurs along the length of the lateral blade and is also developed, though in 
much reduced width, below the posterior bar. 

Remarks. The specimens referred to this species show some variation in the 
development of the callus on the inner lateral face and also in the depth of the lateral 
bar, which tends in some specimens to be deeper in its medial third than its distal 
third. 

Magnilaterella contraria sp. nov. 
Plate 23, figs. 8a-c, i8a-c 

1941 Ligonodina ? sp. Branson & Mehl : 171, PI. 5, fig. 11. 
1963 New Gen. et sp. Rexroad & Collinson : 21, PI. 3, fig. 2. 

Derivation of name. With reference to the morphology. 

Diagnosis. Magnilaterella characterized by very delicate and slender construc- 
tion. Short lateral bar bearing three isolated and recurved denticles, the largest 
being the middle : bar very shallow decreasing in height posteriorly, and making an 
obtuse angle with posterior bar. 

Material. 3 specimens : Holotype X 553, Paratype X 517 (both figured). 

Type locality and horizon. North Crop. Sample 3D 23. 

Range. North Crop 3D 23. 

Description. The lateral bar is short and more or less straight in a vertical plane 
but is strongly recurved, so that its basal surface is continuously concave in lateral 
view. It is of very slender construction and bears only 3 or 4 denticles, the two in 
the medial part being much larger than those at either end. The denticles are 



148 BRITISH AVONIAN CONODONT FAUNAS 

recurved, but their axes are straight and sharply pointed ; they have sharp anterior 
and posterior edges and strongly convex lateral faces, their proximal portions tending 
to become flatter towards their apices ; they are about four to five times as long as 
the other denticles on the unit. The inner lateral face of the lateral bar is marked by 
a callus, which is not conspicuous and does not extend far up the lateral face : the 
bar decreases in width posteriorly and its posterior end is marked by a very small 
denticle, the posterior aboral margin being bluntly rounded ; the bar may be very 
slightly flexed outward in a vertical plane, but it is essentially straight. 

The posterior bar is of unknown length ; it bears at least one small denticle near its 
junction with the lateral bar. It is excavated by a narrow groove which extends 
continuously below the lateral bar. 

Remarks. Rexroad & Collinson (1963 : 21), described forms closely similar to 
this species, but did not include them in the genus Magnilaterella. They did not 
state the reasons for this exclusion, but these presumably involve the relatively 
slight difference in the form of the basal cavity, which in the present specimens tends 
to be medial rather than lateral on the two bars, the restricted nature of the callus, 
and the fact that the posterior denticle of the lateral bar is not the largest of those 
developed. 

Other specimens described above in the present paper show that none of these 
characteristics is wholly distinctive of the genus Magnilaterella. Some species 
which are, on all other morphological criteria, " good " species of the genus, do not 
have the posterior denticle more strongly developed than the rest of the series, and 
the form of the callus is a highly variable feature ; it, therefore, seems to us that there 
is no good reason for excluding this species from the genus. 

Magnilaterella robusta Rexroad & Collinson 
Plate 31, figs. 25, 26, 27 

1941 Lonchodina sp. Branson & Mehl (partim) : 171, PI. 5, fig. 10 only. 

1956 Metalonchodina ? sp. Elias : 124, PI. 5, fig. 3. 

1957 Genus Indeterminate Rexroad (partim) : 42, PI. 4, figs. 19-21 only. 

1958 Genus Indeterminate Rexroad : 26, PI. 5, figs. 1, 2. 

1963 Magnilaterella robusta Rexroad & Collinson : 14, PI. 2, figs. 4, 5, 9, text-figs. 3, 4. 

1964 Magnilaterella robusta Rexroad & Collinson ; Rexroad & Furnish : 673, PI. 111, figs. 

27-3I- 

1965 Magnilaterella robusta Rexroad & Collinson ; Rexroad & Nicoll : 22, 23, PI. 1, figs. 

10, n. 

Material. 3 specimens : figured, X 528, X 529, X 548. 

Range. Scotland Samples DUN 78-79. 

Description. Well preserved specimens from our Scottish faunas are very 
closely similar to those illustrated and described by Rexroad and Collinson. The 
inner lateral process is short and stout, and is strongly recurved and very strongly 
arched. It bears up to 6 denticles, those near the apex being the largest. The 
posterior bar is small and relatively straight. It is strongly flexed and bears only 
1 or 2 denticles, that nearest the anterior end being the largest. 



BRITISH AVONIAN CONODONT FAUNAS 149 

Magnilaterella sp. 

Plate 23, fig. 9 

Material, i specimen : figured, X 244. 

Range. Scotland GILM 2. 

Description. A single specimen of doubtful affinities is referred to this genus. 
It is characterized by the distinctive callus developed on the inner face of the lateral 
bar and the slit-like excavation developed on both bars. The posterior bar is very 
short and may not be broken. The lateral bar bears two denticles which are discrete, 
inclined and sharply pointed ; the bar is broken and is of unknown length. The 
posterior bar bears a single denticle at its junction with the lateral bar ; the denticle 
is short but sharply pointed, being only about one sixth to one seventh the length of 
the posterior bar. 

Magnilaterella spp. 
Plate 23, fig. 10 ; Plate 31, figs. 5, n 

Material. 649 specimens : figured, X 242, X 322, X 323. 
Range. Avon Gorge Z 35-C 24, North Crop CYD 6-3D 17. 

Description. Fragmentary specimens of Magnilaterella are relatively common 
in the upper part of the D Zone and elsewhere. Few of them are sufficiently com- 
plete to enable specific identification, but some of them probably represent new 
species. We illustrate three extreme forms. 

Plate 31, fig. 11 (X 322) shows a form with characteristically deep and strong 
posterior bar, the inner lateral face of which bears a well-developed callus and basal 
groove, which is thin but conspicuous and long. The apical denticle is very strongly 
developed, and has four to five times the basal width of other denticles of the posterior 
bar. The lateral bar is very strongly flexed, and the denticles decrease rapidly in 
size towards the distal end. 

Plate 31, fig. 5 (X 323) shows a form characterized by much more slender construc- 
tion. The apical denticle is elongated and gently curved posteriorly and inwards. 
It is sharply pointed and its general construction is slender. The callus is con- 
spicuous, but shallow, and the lateral bar, which lies at about 90 ° in both a horizontal 
and vertical plane to that of the posterior bar, has its main flexure at its junction with 
the posterior bar rather than being continuously recurved. 

Magnilaterella ? sp. 
Plate 23, figs. 7a, b 

Material, i specimen : figured, X 447. 

Range. North Crop ZLA 37. 

Description. This specimen consists of an antero-lateral and a posterior bar. 
The major denticle is smaller than the denticles on the posterior bar and lies in 



150 BRITISH AVONIAN CONODONT FAUNAS 

between the planes of the two bars. The anterior bar is lateral and deflected, bearing 
3 isolated denticles. The posterior bar bears 3 large, posteriorly inclined denticles. 

Genus MESTOGNATHUS Bischoff 1957 
1957 Mestognathus Bischoff : 36. 

Type species. Mestognathus beckmanni Bischoff 1957. 

Diagnosis. A canoe-shaped form, with a well-developed platform, tapering to 
anterior and posterior. The platform ornamented by numerous transverse ridges. 
A high anterior blade developed on the outer side of the platform ; inner side of the 
platform, in lateral view, extends further to the anterior, than the outer side of the 
platform, because of the development of the anterior blade on the latter. A deep 
trough runs along mid-length of oral surface. Aborally a small narrow basal cavity 
present. 

Remarks. The genus Mestognathus Bischoff closely resembles Cavusgnathus 
Harris & Hollingsworth, but differs from the latter genus in that it has a small 
narrow basal cavity compared with the wide flaring basal cavity typical of Cavus- 
gnathus. Mestognathus has not been recorded from North America and makes its 
first appearance in Europe in Cu II (3/y. In North America Cavusgnathus makes its 
first appearance at nearly the same horizon and so the two genera may be closely 
related. 

Mestognathus beckmanni Bischoff 
Plate 15, figs. 7a-d 

1957 Mestognathus beckmanni Bischoff : 37, PI. 2, figs. 4a, b, c, d, 5, 6, 8, 9. 

i960 Mestognathus beckmanni Bischoff ; Kronberg, Pilger, Scherp & Ziegler : 14, PL 3, 

figs, ia, b. 
1962 Mestognathus beckmanni Bischoff ; Meischner : text-fig. 10. 
1962 Mestognathus beckmanni Bischoff ; Bartenstein & Bischoff : Tab. 3. 

Material. 36 specimens : figured, X 245. 

Range. North Crop CYD 7, Avon Gorge C 15-D 26. 

Description. The carina is restricted to the posterior part of the platform in this 
species, but may in some cases be extended anteriorly to meet the inner lateral face 
at a narrow angle. The anterior blade is high and has from 6 to 12 denticles which 
occupy the anterior margin of the outer side of the platform. The medial trough is 
deep and very wide, and runs for at least half the length of the platform, being 
deepest anteriorly. The unit is about four times as long as it is wide, being widest 
at about mid-length of the platform. In outer lateral view the highest part of the 
anterior blade is about twice the depth of the posterior platform at mid-point. The 
anterior blade is characterized in lateral view by the development of from 6 to 12 
denticles which are basally fused, only their tips being discrete. They tend to be of 
variable size and to have bluntly rounded apices with gently convex lateral faces. 
The largest denticles are the posterior one or two on the blade, especially the most 



BRITISH AVONIAN CONODONT FAUNAS 151 

posterior. This tends to be sub-triangular in form, and is inclined posteriorly, with 
strongly convex lateral faces and blunt anterior and posterior edges. Its inner 
lateral face is flatter than its outer. The other denticles stand more or less erect to 
the bar but their inclination is rather variable. The anterior blade is inclined gently 
inwards ; there is a tendency for the denticles, to show some reduction in height 
anteriorly and the anterior blade projects beyond the platform at the anterior end. 
In oral view a deep trough is developed parallel to the anterior blade, being widest 
and deepest anteriorly. It shallows towards the position of maximum width of the 
posterior platform and becomes obsolescent in the posterior half. It is broadly U- 
shaped. The outer margins of the carina are decorated with feeble to moderate 
transverse ornament, which tends to be aligned acutely to the length of the unit, 
forming an arrow-type structure pointing forward, rather than being developed at 
right angles. There are about 12 of these ridges on the outer side of the platform 
and about 17 on the inner. They become rapidly obsolescent towards the middle of 
the platform and are more feebly developed on the inner than on the outer side. 
There is a variable posterior carina developed in the posterior part of the unit, 
consisting of a low ridge of only barely distinguishable nodose denticles, but it may be 
extended anteriorly to meet the antero-lateral inner edge of the platform as a low 
inconspicuous ridge, dividing the platform into two unequal parts. It runs to the 
left of the medial trough. The outline of the platform in oral view is such that the 
anterior two-thirds of the inner lateral margin is straight and the posterior third 
inclined towards its pointed posterior termination. The outer lateral face is straight 
in its anterior half and gently concave in its posterior half, the whole appearance of 
the unit being pinched towards the posterior fifth. The anterior inner lateral edge 
terminates in an undenticulate projection. The edges of the platform are feebly up- 
turned. In inner lateral view the antero-inner face of the platform is flat, with sharp 
oral and aboral lateral edges. The lateral face decreases in width towards the mid- 
point, beyond which the platform has a thin lateral face which merges with the base. 
The outer lateral face is characterized by having a flat surface, parallel to the 
denticles, with a longitudinal ridge developed about the base of them, and then a 
sloping lateral face which slopes towards the basal cavity below the ridge. In outer 
lateral view the posterior half has a lateral face, which slopes steadily towards the 
basal cavity. 



Anterior blade Outerslde of platform 



Anterior 




Platform 

Carina Posterior 



Inner lateral face 

v Trough 

Fig. 30. Mestognathus sp. showing morphological terms used in the text. 



152 BRITISH AVONIAN CONODONT FAUNAS 

The basal surface is characterized by a restricted median cavity, which is shallow 
and occupies the anterior half of the platform. It extends anteriorly and posteriorly 
as a very narrow shallow slit along the unit. 

Mestognathus bipluti Higgins 

Plate 25, figs. ia-3c, 8a, b 

1961 Mestognathus bipluti Higgins : 216, PI. 10, figs. 1, 2 ; text-fig. 4. 

Diagnosis. This species is characterized by a short, deep blade which diverges at 
the anterior end of the unit from the antero-inner lateral edge of the platform. 
Slender and pointed platform has a more or less prominent median carina. 

Material. 3 specimens : figured, X 249, X 248, X 246, X 247. 

Range. North Crop CYD 6-CYD 7. 

Description. This species of conodont has an outline that is reminiscent to some 
extent of a folsom-point. The inner edge of the platform is straight in the anterior 
two thirds and then turns rapidly inwards towards the pointed posterior end. The 
posterior third is also straight and the bend is sharply angular. The outer lateral 
margin of the platform is straight in its anterior third and up to the end of the 
anterior blade, but posteriorly it is turned sharply inwards towards the pointed 
posterior end. The posterior outer lateral face is more or less straight. There is a 
strongly developed posterior carina, which consists of a series of confluent nodes, and 
extends about half the length of the platform. It is continued less obviously 
anteriorly to meet the antero-inner lateral point as a low inconspicuous ridge. There 
is a narrow deep trough adjacent to the blade and this becomes shallower and 
obsolescent posteriorly, extending on the outer side of the median carina. The inner 
lateral portion of the platform adjacent to the carina tends to be flat or feebly con- 
cave. The margins of the platform are ornamented by relatively strongly developed 
transverse ridges, which tend to become less conspicuous towards the posterior end. 
They extend about half the distance from the lateral margins to the carina. The 
lateral margins themselves are gently up-flexed. The downward and outward 
curvature of the antero-aboral portion of the blade is a conspicuous feature in oral 
view, as is the divergence of the anterior blade and the antero-inner edge of the 
platform to give a branched structure. 

In aboral view this latter feature is the most conspicuous characteristic of the 
species. The total length of the branches are a third to a quarter of the length of the 
platform. The medial cavity is very small and inconspicuous and is only slightly 
flared. It extends anteriorly and posteriorly as a keeled narrow slit along the 
median line of the unit. The main cavity is situated near the junction of the blade. 

In inner lateral view the oral surface of the unit is bluntly serrated and the posterior 
end is bluntly spatulate. In outer lateral view the aboral margin is straight in 
the posterior half, but gently concave in the anterior half. In outer lateral view 
the anterior blade is a very distinctive feature. The posterior denticle is the largest 
and the blade decreases regularly in depth towards the bluntly spatulate anterior end. 



BRITISH AVONIAN CONODONT FAUNAS 153 

The denticles form a fused series of bluntly pointed confluent denticles, about 5 or 
6 in number, grading in the antero-aboral region into minute and inconspicuous 
confluent denticles. The antero-aboral portion is flexed sharply outwards ; the 
posterior denticle is inclined slightly posteriorly. The whole posterior outer lateral 
face of the platform slopes gently inwards to meet the basal slit, giving a boat-like 
appearance to the unit in lateral view. It is convex to flat in its upper part and may 
become concave in its postero-aboral portion. In inner lateral view the same feature 
is seen. The platform is relatively straight in its posterior third, but is regularly 
concave in its anterior third or half. The inner lateral margin is generally developed 
at a lower level than the outer lateral margin, and is finely denticulated, the inner 
anterior edge of the platform bearing rather conspicuous low denticles. The antero- 
aboral inner edge is strongly convex and is deflected inwards. It is much less deep 
than the corresponding outer aboral anterior edge. 



Mestognathus neddensis sp. 

Plate 15, figs. 4a-6c 



nov. 



Derivation of name. From the River Nedd, Breconshire. 

Diagnosis. Mestognathid with short deep anterior blade, bearing 6 denticles, 
those at anterior end being only slightly shorter than those at posterior ; their apices 
are discrete. Anterior blade and inner anterior edge of platform bifurcate at the 
anterior end of the unit. Posterior platform straight on outer lateral side and gently 
convex on inner lateral side, posterior inner lateral portion being strongly pinched 
inwards towards pointed posterior end. Strong posterior carina, consisting of low 
rounded nodes along posterior half of platform, becoming obsolescent towards 
anterior inner lateral edge of platform. 

Material. 5 specimens : Holotype X 250, Paratypes X 251, X 252 (all figured). 

Type locality and horizon. North Crop. Sample CYD 6. 

Range. North Crop CYD 6-CYD 7. 

Description. In oral view the unit is elongated and slender. The anterior blade 
is free for only a very small portion of its length, but the anterior end of the platform 
is marked by a V-shaped indentation, formed by the junction of the anterior blade 
and the inner anterior margin of the platform. The blade is conspicuously denticu- 
lated in oral view and the outer lateral margin of the platform is more or less straight. 
It is ornamented by a series of transverse denticles which are more strongly developed 
in the anterior portion than "the posterior. The inner lateral platform is gently 
sinuous, being straight to gently concave in the anterior third and strongly convex in 
the posterior two thirds. The posterior carina extends beyond the posterior limit 
of the platform, so the whole appearance of the platform is rather pinched posteriorly. 
The inner lateral margin of the platform is ornamented by feeble, nodular to trans- 
verse ridges which become obsolescent towards the anterior part. The posterior 
half of the platform is marked by a conspicuous carina, consisting of 7 or 8 low 
rounded fused nodes, and is extended as a rather inconspicuous ridge towards the 



154 BRITISH AVONIAN CONODONT FAUNAS 

anterior inner lateral edge of the unit. There is a narrow V-shaped trough developed 
adjacent to the blade, running towards the posterior end of the unit on the outer 
margin of the carina, and becoming shallower and narrower posteriorly. In outer 
lateral view the blade is conspicuously deeper than the platform. It is of regular 
depth throughout its length and in some specimens shows a tendency to increase 
anteriorly in depth. It is very bluntly rounded antero-aborally, and is strongly 
down-flexed in relation to the blade. Although the junction between the two is 
curved, the anterior aboral edge of the blade makes an angle of about 45 ° with the 
aboral edge of the posterior platform. The oral surface of the blade bears 6 or 7 
fused denticles, the apical tips of which are discrete and bluntly rounded. 

In outer lateral view the posterior platform has a bluntly serrated surface and its 
outer lateral face slopes down sharply towards the median aboral keel. The 
posterior end is more or less flat, and the denticles of the posterior median carina tend 
to be higher in outer lateral view than those on the edge of the platform. The 
posterior third of the platform is straight, but the anterior part is gently concave. 
The denticles of the anterior blade are more or less uniform in height, although the 
most posterior tends in some specimens to be rather larger than the rest. They are 
more or less erect, though the most posterior denticle may be slightly inclined 
posteriorly. 

In inner lateral view the aboral surface of the whole unit appears to be gently 
convex, except for the rather straight posterior termination. The oral edge is more 
or less conspicuously serrated by low nodose confluent nodes, and the anterior inner 
edge is frequently developed into one or two rather conspicuous denticles, its antero- 
aboral margin being bluntly pointed and making a very prominent bifid junction with 
the anterior blade. The extension of the posterior carina is a prominent feature in 
this inner lateral view. The inner oral margin of the platform is strongly convex, 
but it flattens off along the mid-height of the unit, and the lower part is flat to 
strongly concave, sloping rapidly towards the elongated aboral keel. 

In aboral view there is a prominent, but very small, median pit with inconspicuous 
edges, which is developed near the junction of the blade of the platform. It is 
biconvex in outline and is elongated antero-posteriorly. A shallow rather flat aboral 
surface extends posteriorly from it along the unit with an inconspicuous median slit 
developed towards the posterior end. Anteriorly a thin slit runs towards the 
junction of the inner anterior edge with the anterior blade. 

The posterior end of the platform is marked by a more or less vertical face, with 
rounded posterior aboral margin. The platform deepens towards the anterior inner 
edge when seen in inner lateral view, and this is a conspicuous feature of the unit. 

Genus METALONCHODINA Branson & Mehl 1941 
Type species. Prioniodus bidentatus Gunnell 193 1. 

Metalonchodina bidentata (Gunnell) 
Plate 24, figs. 8a-nb 
1900 Polygnathus convexus Hinde (partim) : 342, PI. 9, fig. 8. 



BRITISH AVONIAN CONODONT FAUNAS 155 

1928 Lonchodus convexus (Hinde) Holmes (partim) : 14, PI. 6, fig. 13. 

1931 Prioniodus bidentatus Gunnell 247, PL 29, fig. 6. 

1933 Prioniodus dactylodus Gunnell 265, PI. 31, fig. 1. 

1941 Metalonchodina bidentata (Gunnell) Branson & Mehl : 106, PI. 19, fig. 34. 

1941 Metalognathus bidentata (Gunnell) Ellison : 116, PI. 20, figs. 35, 36. 

1952 Metalognathus bidentata (Gunnell) Rhodes : 898, PI. 128 ' m '. 

1957 Metalonchodina bidentata (Gunnell) Bischoff : 37, PI. 5, figs. 13, 15, 46. 

i960 Metalonchodina conflecta Clarke : 17, PI. 2, fig. 14. 

1961 Metalonchodina bidentata (Branson & Mehl) Higgins : PI. 12, fig. 9. 

1962 Metalonchodina bidentata (Gunnell) Higgins : PI. 1, fig. 3. 
1964 Lonchodina ? nipponica Igo & Koike : 186, PI. 27, fig. 20. 

1964 Metalonchodina sp. Rexroad & Furnish : 673, PI. 111, fig. 7. 

1965 Metalonchodina fragilis Murray & Chronic : 605, PI. 73, figs. 19, 20. 
Metalonchodina bidentata (Gunnell) Collinson & Druce (in press). 

Material. 6 specimens : figured, X 253, X 254, X 255, X 256. 

Range. North Crop 3D 10-3D 14/15. 

Description. The present specimens agree closely with Branson & Mehl's 
(1941 : 106) definition of the species. The anterior limb is shorter than the posterior 
bar and bears a massive denticle or pair of denticles upon it. In aboral view the 
most conspicuous feature is the very strong lateral flexing below the apex of the two 
bars. The small and fairly shallow pit is situated in the middle of the strongly 
laterally expanded aboral surfaces at this point ; the aboral surfaces of each limb 
being relatively flat or obtusely V-shaped. They are excavated by very narrow 
shallow slit-like cavities along their lengths. The chief expansion of the base below 
the apical denticle is concentrated on the inner lateral side and is a very prominent 
feature of the unit. In inner lateral view the most conspicuous feature of the unit is 
the enormous size of the denticle developed on the anterior bar. This is about two 
to three times as wide as any of the other denticles, has straight anterior and posterior 
edges and is bluntly pointed. It has gently convex inner and outer lateral faces. 
The anterior edge of the unit is developed into a triangular pointed anterior end. Its 
aboral margin is straight, and although its junction with the posterior bar is curved, 
it makes an angle of 80 °-o,o ° with the aboral surface of the latter. The posterior bar 
bears two or three smaller denticles, sub-circular in cross-section, with inconspicuous 
anterior and posterior edges, which are inclined anteriorly. 



Apical denticle 

-Main denticle 




Inner loterol 

aboral expansion ./v ""^"\;J ' Anterior limb 



Posterior bor V N Aboral margin 

Fig. 31. Metalonchodina sp. showing morphological terms used in the text. 



156 BRITISH AVONIAN CONODONT FAUNAS 

The apical denticle is smaller than the large denticle on the anterior bar but of 
similar general form. Its most conspicuous feature is the very strong, internal lateral 
extension of the aboral portion, to form the inner lateral flange. On the aboral 
margins both the anterior and the posterior bars are more or less straight. Their 
most striking feature in inner lateral view is the development of a longitudinal ridge 
parallel to their bases, which rises higher on the faces towards the apex, and 
represents the bevelled margin of the flattened aboral surface. 

In lateral view this latter feature is less conspicuous and the whole unit is flat to 
feebly convex in general form. 

Remarks. This species shows appreciable variation. The specimens illustrated 
in PI. 24, figs. 8, 10 and n are closely similar. That of PI. 24, fig. 9, resembles them 
in overall form but has an additional denticle developed anterior to the main denticle 
of the anterior bar, and the apical and posterior denticles also tend to be more sub- 
circular than those of typical members of the species. Similarly, other specimens 
have two smaller denticles developed anterior to the main denticle of the anterior bar 
and also have more sub-circular denticles. It may be that these specimens should be 
regarded as distinct species but they are provisionally included in Metalonchodina 
bidentata. 



Genus NEOPRIONIODUS Rhodes & Muller 1956 

1956 Neoprioniodus Rhodes & Muller : 698. 
Type species. Prioniodus conjunctus Gunnell 1931. 



Neoprioniodus antespathatus Collinson & Druce 
Plate 21, figs, ioa-nb 
Neoprioniodus antespathatus Collinson & Druce (in press). 

Material. 2 specimens : figured, X 257, X 258. 

Range. North Crop 3D 8-3D 16. 

Description. This is a neoprioniodid with a slender anteriorly directed anterior 
denticle, with sharp anterior edge, blunt posterior edge, and biconvex outline. The 
posterior bar is slender, decreasing in depth posteriorly, and it has a conspicuously 
concave junction with the aboral process. Its oral surface bears a series of about 9 
denticles, the largest of which are in the anterior half, and which show a broad 
tendency to decrease in size posteriorly, though this tendency is not conspicuous or 
regular. The denticles are basally confluent, but are discrete for most of their 
length. They are of slender general form, with sharp anterior and posterior edges 



BRITISH AVONIAN CONODONT FAUNAS 



157 



and gently convex lateral faces. They stand more or less erect or gently posteriorly 
inclined in relation to the underlying aboral surface of the bar. The posterior bar is 
gently down-curved, although its distal portion is more or less straight. The aboral 
projection of the anterior denticle is the most massive feature of the unit. It is 
about twice as wide in lateral view as the basal part of the anterior denticle itself. 
Its anterior margin is straight to very gently concave and its anterior aboral termina- 
tion is bluntly pointed. Its posterior aboral margin is very strongly convex and it 
decreases in width towards its distal end. The whole effect is of a massive structure. 
Its lateral faces are more or less flat but the whole unit is feebly curved inwardly. 

In outer lateral view the whole unit is convex, reflecting the inward recurvature. 
In aboral view there is a very inconspicuous cavity developed below the apical 
denticle ; the aboral surfaces of the posterior bar and the aboral process are flat in 
general form, the inner lateral aboral edge being slightly higher than the lower, and 
the whole surface is excavated by a minutely narrow and shallow longitudinal groove. 

The most conspicuous features of this unit are the slender form of the anterior 
denticle and the posterior bar, in contrast to the massive form of the aboral process, 
the whole anterior lateral aboral face of which is more or less concave. 



Anterior denticle 



Anterior edge 



Anterior 



Aboral 
process 




Denticles of posterior bar 



Posterior 



Posterior bar 



Aboral edge 



Fig. 32. Neoprioniodus sp. showing morphological terms used in the text. 



158 BRITISH AVONIAN CONODONT FAUNAS 

Neoprioniodus barbatus (Branson & Mehl) 
Plate 21, figs. 4-7 

1934 Prioniodus barbatus Branson & Mehl : 288, PI. 23, figs. 19, 20. 

1934 Prioniodus corniger E. R. Branson : 329, PI. 28, fig. 2. 

1938 Prioniodus barbatus Branson & Mehl ; Branson & Mehl : 144, PI. 33, fig. 21, pi. 34, 

figs. 28, 32. 

1938 Prioniodus corniger (?) E. R. Branson ; Branson & Mehl : 143, PI. 34, fig. 19. 

1944 Prioniodus barbatus Branson & Mehl ; E. B. Branson : 221, PI. 39, figs. 28, 32. 

1944 Prioniodus corniger (?) E. R. Branson ; E. B. Branson : 221, PI. 39, fig. 19. 

1949 Prioniodus barbatus Branson & Mehl ; Thomas : 411, PI. 4, fig. 26. 

1949 Prioniodus corniger E. R. Branson ; Thomas : 411, PI. 4, fig. 27. 

1956 Prioniodina barbata (Branson & Mehl) Bischoff & Ziegler : 160, PI. 13, figs. 19, 20. 

Material. 674 specimens : figured, X 259, X 260, X 261, X 262. 
Range. North Crop KL 13-ZL 9, Avon Gorge K 21-C 16. 

Description. The anterior denticle is very tall, slender, laterally compressed, and 
ovate in cross-section. It is continuously and gently recurved toward the posterior, 
terminating in a fine point. The posterior bar is fairly deep, being deepest at the 
anterior and shallowing regularly towards the posterior. It bears 9 to 12 tall needle- 
like denticles, sub-circular in cross-section, which are fused at their bases but free at 
their tips. In the posterior part there is some twisting of the bar and it is down- 
curved slightly. 

The basal cavity is situated on the aboro-posterior side of the anterior denticle, 
which is produced below the posterior bar to form an aboral process. The complete 
aboro-posterior surface is excavated, though there is comparatively little flaring of 
the lips, and the cavity may run for a short distance beneath the posterior bar. In 
most specimens the aboro-posterior outline of the aboral process is gently convex, 
but in some specimens a flange tends to develop, making it sigmoidal in outline 
(e.g. PI. 21, fig. 6). 

Remarks. This appears to be a very common Avonian species, especially in the 
middle of the Z Zone. 



Neoprioniodus confluens (Branson & Mehl) 
Plate 21, figs. 2a, b, 8a, b 

1934 Prioniodus confluens Branson & Mehl (partim) : 206, PI. 15, fig. 6, (non PI. 15, fig. j = N. 

alatus) . 
1934 Euprioniodina prona Huddle (partim) : 52, PI. 6, fig. 19, (non PI. 11, fig. 8 = Euprioniodina 

alternata) . 
1939 Prioniodus alatus Hinde ; Cooper : 404, PL 46, figs. 6, 8. 
1949 Prioniodus apkanes (Cooper) Thomas : 411, PL 4, figs. 20, 34. 
1949 Prioniodus obtusus Branson & Mehl ; Thomas 408, PI. 1, figs. 1, 7. 
1955 Prioniodus prona (Huddle) Sannemann (partim) : 152, PL 3, fig. 1 only. 
1957 Prioniodina prona (Huddle) Ziegler in Fliigel & Ziegler : 49, PL 4, fig. 6. 
1 961 Neoprioniodus armata (Hinde) Scott & Collinson (partim) : 127, PL 2, fig. 24, (non 

PI. 2, fig. 22 = iV. armata). 



BRITISH AVONIAN CONODONT FAUNAS 159 

Lectotype (here selected). The original of Branson & Mehl : 1934, 206 ; PI. 15, 
fig. 6 only, University of Missouri C 365-5. 

Material. 672 specimens : figured, X 264, X 263. 

Range. North Crop KL i-ZLA 33, Avon Gorge K 3-C 7. 

Description. The anterior denticle is tall and narrows gradually to a pointed 
extremity. It is produced aborally into an aboral process. The posterior bar, which 
is straight or gently down-curved, is also deflected through 45 ° and slightly twisted. 
It bears a series of erect laterally compressed denticles, which are either fused or are 
in close proximity. The bar is very long and may possess up to 40 denticles which 
alternate in size. The basal cavity is situated at the junction of the posterior bar and 
the aboral process. It has a flared lip to produce a characteristic flange. 

Remarks. This is one of the most easily recognizable neoprioniodids owing to the 
large aboral process of mature specimens and the cavity flange. Frequently only the 
anterior denticle and cavity flange are preserved. Branson & Mehl (1934 : 206) 
described two co-types of the species Prioniodus confluens (Catalogue numbers 
C 365-5, University of Missouri). These appear to represent different species and 
we hereby designate the specimen illustrated in PI. 15, fig. 6, as the lectotype of 
Neoprioniodus confluens (Branson & Mehl). This is given the same Catalogue 
Number as the other co-type (C 364-5). 

One specimen (PL 21, figs, ia-c) shows extreme regularity of dentition and it is 
only tentatively compared with this species. 

Neoprioniodus conjunctus (Gunnell) 
Plate 21, figs. i6a-i7b, 20a, b 

1926 Prioniodus sp. B (Roundy) (partim) : n, PI. 4, fig. 12 only. 

1 93 1 Prioniodus conjunctus Gunnell : 247, PI. 29, fig. 7. 

1933 Prioniodus cacti Gunnell : 263, 265, 267, PI. 31, figs. 4 to 5. 

1933 Prioniodus sp. Gunnell : 264, 267, PI. 32, fig. 32. 

1941 Prioniodus conjunctus Gunnell ; Ellison : 108-111, 113, 114, PI. 20, figs. 1—3, 16. 

1941 Prioniodus bulbosus Ellison : 108-111, PI. 20, figs. 4-7. 

1944 Prioniodus conjunctus Gunnell ; E. R. Branson : 327. 

1949 Prioniodus cacti Gunnell ; Youngquist & Downs : 169, PI. 30, figs. 16, 17. 

1953 Prioniodus inclinatus Hass : 87, PI. 16, figs. 10-14. 

1956 Neoprioniodus conjunctus (Gunnell) Rhodes & Miiller : 3. 

1957 Prioniodina bulbosa (Ellison) Bischoff : 46, PI. 5, fig. 37. 
i960 Neoprioniodus brevis Clarke : 13, 14, PI. 2, fig. 7. 

1961 Neoprioniodus inclinatus (Hass) Higgins : 220, PI. 11, fig. 3. 

1962 Neoprioniodus conjunctus (Gunnell) ; Higgins : 10, PI. 1, fig. 2. 

Material. 7 specimens : figured, X 265, X 267, X 266. 

Range. North Crop 3D 14/15, Avon Gorge Z 35-C 7. 

Description. The present specimens agree perfectly with Gunnell's holotype and 
with Ellison's (1961) descriptions and illustrations. The massive, blade-like anterior 
denticle, with the deep posterior bar consisting of confluent, strong denticles, up to 
about 4 in number, are very conspicuous features of the species. However, the 



160 BRITISH AVONIAN CONODONT FAUNAS 

posterior bar is strongly laterally compressed and is relatively thin, being more or less 
triangular in section, with the aboral edge being the widest. The lateral faces are 
flat to feebly concave. The denticles of the posterior bar are strongly laterally com- 
pressed and are confluent for most of their length. They are bluntly pointed and 
have more or less sharp anterior and posterior edges, their lateral faces being feebly 
biconvex. The denticles proper are about twice the length of the posterior bar. 
The anterior denticle is very strongly developed ; it is massive in general form, being 
about five times the length and two or three times the width of the largest denticles 
of the posterior bar. It is slightly recurved posteriorly, but its distal portion is more 
or less straight. It has very sharp anterior and posterior edges and is so strongly 
compressed in lateral view that it has a sword-like appearance. It is bluntly 
pointed. Its inner aboral lateral face is very strongly extended inwards, and this is 
a most conspicuous feature of the unit in lateral view. Its outer lateral face is feebly 
convex to flat in the lower part and is gently convex in the upper portion. The 
whole unit is very slightly curved in a horizontal plane, the inner side being feebly 
concave. In aboral view the most striking feature is the wide flaring of the inner 
lateral aboral edge around the junction of the anterior denticle and the posterior bar. 
The outer lateral face is less conspicuously flared. The whole aboral surface below 
this lateral flexure is excavated, culminating in a deep median pit which is restricted 
in its area, but extends anteriorly and posteriorly as rather conspicuous longitudinal 
grooves along the anterior portion of the anterior denticle and along the posterior 
bar. The posterior aboral edge of the anterior denticle makes an angle of about 120 ° 
with the straight edge of the posterior bar. The antero-aboral corner is very slightly 
convex and the junction with the edge is more or less pointed. 



Neoprioniodus montanaensis (Scott) 
Plate 22, figs. 5a-8b 

1942 Lochreia montanaensis Scott (partim) : 289, PI. 29, fig. 9 only, PI. 40, fig. 12. 

1 94 1 Prioniodus barbatus Branson & Mehl ; Ellison & Graves (partim) : 3-4, PI. 1, fig. 25 

only. 

1953 Prioniodus singularis Hass : 88, PI. 16, fig. 4. 

1956 Prioniodus cf. singularis Hass ; Elias : 112, PI. 2, fig. 45. 

1956 Prioniodus roundyi var. dividen Elias : no, PI. 2, figs. 39-41. 

1957 Prioniodina alatoidea (Cooper) Bischofl : 45, PI. 5, figs. 33, 34, 36. 

1957 Prioniodus sp. A Ziegler in Fliigel & Ziegler : 50, PI. 4, fig. 3. 

1958 Neoprioniodus singularis (Hass) Stanley : 471, PI. 66, figs. 2, 3. 
1958 Neoprioniodus sp. A Stanley : 472, PI. 66, figs. 4, 5. 

1961 Neoprioniodus singularis (Hass) Higgins : PI. n, fig. 5. 

1962 Neoprioniodus singularis (Hass) Higgins : PI. 1, fig. 8. 

1963 Neoprioniodus singularis (Hass) Bouckaert & Higgins : 17, fig. 3. 
Neoprioniodus singularis (Hass) Collinson & Druce (in press). 

Material. 232 specimens : figured, X 268, X 270, X 269, X 271. 

Range. North Crop CYD 6-3D 19. 

Description. The most distinctive feature of this species is the long, slender, 



BRITISH AVONIAN CONODONT FAUNAS 161 

blade-like anterior denticle, which is enormously elongated in comparison with its 
rather slight aboral process. The latter is only about one-sixth to one-seventh the 
total length of the denticle. The posterior bar is also conspicuous, being short and 
sharply down-curved. The denticles of the posterior bar show a sharp decrease in 
length towards the posterior end of the bar. Those adjacent to the anterior denticle 
tend to be greatly elongated in comparison with those that follow. All are slender, 
with more or less sharp anterior and posterior edges, and gently convex lateral faces. 
They are discrete for about half their length and are regularly pointed. The whole 
unit is more or less strongly curved inwards in a horizontal plane. 

The anterior denticle is greatly elongated and is very slender in its general form, 
being bluntly to sharply pointed at its apical tip. It extends as an aboral process 
only for a short distance, about one-sixth to one-seventh of its total length, below the 
level of the posterior bar. The anterior and posterior edges are generally straight, 
though in a few specimens they may be feebly recurved, and in other specimens there 
is a very slight anterior flexure of the aboral process. The anterior denticle has 
sharp anterior and posterior edges and gently convex lateral faces. It stands erect 
to the anterior portion of the posterior bar. The aboral process is more or less 
sharply pointed and triangular in form, without any conspicuous lateral flaring 
developed on the inner aboral margin. The anterior denticle is slightly curved 
inward in its distal third. The denticles of the posterior bar range from 10 to 21 in 
number and show a marked decrease in size posteriorly. The 2 adjacent to the 
anterior denticle are virtually confluent with it, only their apices being discrete. 
The remaining denticles of the posterior bar tend to be smaller and to be inclined 
more sharply posteriorly. They are discrete for about half their total length in 
complete specimens. The posterior bar shows a marked decrease in depth from the 
anterior to the posterior end. The posterior terminus is bluntly rounded. It has 
more or less flat to gently convex lateral faces, and a sharply bevelled aboral margin 
on both the inner and outer lateral faces. The whole unit is recurved inwardly in a 
horizontal plane. There is a relatively inconspicuous cavity below the anterior 
denticle, which extends as a shallow slit along the posterior bar and the antero-aboral 
process. 

Remarks. Hass (1953 : 88) erected the species Prioniodus singularis to include 
the present specimens. However, because the species was illustrated and described 
by Scott, even as part of a natural assemblage, it seems to us that his name must have 
priority. We, therefore, regard Prioniodus singularis Hass (1953 : 88, PI. 16, fig. 4) 
as a junior synonym of Scott's species. 

Neoprioniodus peracutus (Hinde) 
Plate 21, figs. I2a-i5b 

1900 Prioniodus peracutus Hinde (partim) : 343, PI. io, fig. 22 only. 

1926 Prioniodus peracutus Hinde ; Roundy : io, PI. 4, fig. 6. 

1928 Prioniodus peracutus Hinde ; Holmes : 21, PI. 3, fig. 38. 

1953 Prioniodus ligo Hass : 87, PI. 16, figs. 1-3. 

1957 Neoprioniodus erectus Rexroad : 34, PI. 2, figs. 23, 25. 



162 BRITISH AVONIAN CONODONT FAUNAS 

1957 Prioniodina cassilaris (Branson & Mehl) BischofT : 46, PI. 5, figs. 27-31. 

i960 N eoprioniodus peracntus (Hincle) Clarke : 14, PI. 2, fig. 6. 

1964 N eoprioniodus peraculus (Hinde) Rexroad & Furnish : 674, PI. m, fig. 25. 

Material. 32 specimens : figured, X 272, X 273, X 274, X 275. 
Range. North Crop 3D 4-3D 22. 

Description. A slender neoprioniodid in which the anterior denticle is continued 
more or less vertically downward to form the aboral process. There is a slender and 
highly recurved posterior bar, the straight postero-aboral portion of which makes an 
angle of about 130 ° with the posterior edge of the anterior denticle. The posterior 
bar decreases in depth posteriorly, its posterior termination being bluntly pointed, 
its antero-aboral surfaces gently concave, and its postero-aboral surface gently 
convex in lateral view. In outer lateral view its face is flat, and the whole unit is 
curved slightly inward so that its inner margin is concave. The oral surface of the 
posterior bar bears about 19 denticles which tend to decrease in height posteriorly. 
They are basally confluent, but apically discrete, being bluntly pointed, with sharp 
anterior and posterior edges and convex lateral faces. The denticles tend to be most 
conspicuously discrete in the anterior third of the bar, those towards the posterior 
portion being coalesced for the greater part of their length, but being discrete in their 
apical region. 

The anterior denticle is slightly offset inwardly from the main line of the posterior 
denticles. It has sharp anterior and posterior edges, a feebly convex outer lateral 
face, and a rather flat antero-inner surface which extends downwards into the flat 
aboral process. The anterior edge of the aboral process is more or less straight, and 
the posterior aboral edge is regularly but feebly convex, giving the whole aboral 
extension a slender plough-like appearance. In inner lateral view, the inward 
deflection and curvature of the anterior denticle are well seen ; the antero-aboral 
face of the anterior denticle tends to be slightly concave, but otherwise the inner 
lateral face is more or less flat to feebly convex in its upper portion. Its anterior 
aboral edge bears two minor irregularities, but these are not sufficiently distinct to be 
recognized as denticles. The interior aboral edge of the anterior denticle is 
expanded, but not strongly so, and there is a very shallow longitudinal pit developed 
which extends along the flattened basal surface of the posterior bar ; the anterior 
part of the denticle has longitudinal slit-like grooves. 

Neoprioniodus scitulus (Branson & Mehl) 
Plate, 22, figs, cja-iob, 12a, b 

1939 Prioniodus peracutus Cooper : 406, PI. 46, fig. 7. 

1940 Prioniodus scitulus Branson & Mehl : 173, PI. 5, figs. 5, 6. 

1947 Prioniodus scitulus Branson & Mehl ; Cooper : 92, PI. 20, figs. 1-3. 
1949 Prioniodus spp. Youngquist & Miller : 62, PI. 101, figs. 9, 10, 14. 

1956 Prioniodus scitulus Branson & Mehl ; Elias : 109, PL 2, figs. 9, 10. 

*957 Neoprioniodus scitulus (Branson & Mehl) Rexroad : 35, PL 2, figs. 22, 26. 
J957 Neoprioniodus striatus (Branson & Mehl) Rexroad : 35, PI. 2, figs. 11, 12. 

1957 Prioniodina cassilaris Branson & Mehl ; Bischoff : 46, 47, PI. 5, figs. 27-31. 



BRITISH AVONIAN CONODONT FAUNAS 163 

1958 Neoprioniodus scitulus (Branson & Mehl) Rexroad : 23, 24, PI. 5, figs. 10-14. 

J 959 Neoprioniodus scitulus (Branson & Mehl) Elias : 151, PI. 2, figs. 6, 7. 

*959 Neoprioniodus cassilaris (Branson & Mehl) Elias : 153, PI. 2, figs. 20, 21 only. 

1961 Neoprioniodus scitulus (Branson & Mehl) Higgins : 220, PI. 11, fig. 1. 

1961 Neoprioniodus scitulus (Branson & Mehl) Rexroad & Burton : 1155, PI. 140, figs. 15-17. 

1963 Neoprioniodus scitulus (Branson & Mehl) Bouckaert & Higgins : 17, fig. 3. 

1963 Neoprioniodus scitulus (Branson & Mehl) Thompson & Goebel : 12, fig. 3. 

1964 Neoprioniodus scitulus (Branson & Mehl) Rexroad & Furnish : 674, PI. 111, figs. 36, 37. 

1965 Neoprioniodus scitulus (Branson & Mehl) Rexroad & Nicoll : 23, 24, PI. 2, figs. 21, 22. 
Neoprioniodus scitulus (Branson & Mehl) Collinson & Druce (in press), PI. 2, fig. 1. 

Material. 24 specimens : figured, X 276, X 277, X 278. 

Range. North Crop 3D 2-3D 14/15. 

Description. This is a variable species which, as Rexroad (1958 : 23) has 
demonstrated, shows appreciable variation during ontogeny in the relative curvature 
of the anterior denticle, the length of the aboral projection and the outline of the 
aboral margin. The basal cavity is also variable, and tends to be filled in during 
growth, ultimately resulting in a minute pit, with a longitudinal median groove 
extending anteriorly and posteriorly from it. There are also smaller differences in 
the form and denticulation of the posterior bar, which are shown by numbers of well- 
preserved specimens in the present faunas. In younger individuals the posterior 
inclination of the denticles of the posterior bar tends to be correspondingly greater 
than that in older individuals, but this, as well as the other variations, seem to fall 
within the limits of Branson & Mehl's species. 

Remarks. The variation in " another prioniodid " mentioned by Branson & 
Mehl (1940 : 174) as including a minute pit and attachment scars on the lateral faces 
of the anterior denticle, seem to fall within the variation of the present species, 
rather than representing a distinct species as they suggest. The most striking 
general features of the present species are the long slender elegant anterior denticle, 
the rather short finely pointed aboral process, and the relatively slender, straight to 
slightly curved posterior bar, together with a general lack of flaring in the lateral 
faces below the anterior denticle. 

Neoprioniodus spathatus Higgins 
Plate 21, figs. 9a, b 
1961 Neoprioniodus spathatus Higgins : 217, PI. 11, figs. 2, 4, text-fig. 5. 
Material, i specimen : figured, X 279. 
Range. North Crop 3D 14/15. 

Description. The diagnostic feature of this species is the spatulate plough-like 
form of the aboral process, which projects with conspicuously concave lateral faces 
and strongly laterally extended basal surfaces. It has a denticulated anterior edge. 

The anterior denticle is relatively strongly developed. Its inner lateral face is flat 
to very feebly convex, but its outer lateral face is more strongly convex. It has very 
sharp anterior and posterior edges and is laterally twisted and slightly inwardly 



i6 4 BRITISH AVONIAN CONODONT FAUNAS 

recurved in its upper portion. In inner lateral view, it is concave in its anterior 
proximal portion and feebly convex in its posterior proximal portion. It is elongated 
and more or less sharply pointed, the anterior and posterior edges being straight. 
The aboral process is strongly developed, with a concave to straight anterior margin, 
and a continuously convex posterior margin. Its lateral faces are flat in the anterior 
portion, but the base of the inner lateral side is strongly flared to give a conspicuously 
spatulate appearance. Its anterior edge has 2 or 3 minute denticles developed on it 
which are of smaller size than any on the posterior bar. 

The posterior bar is short and relatively deep. It bears more than 6 denticles, 
which are more or less erect or only slightly posteriorly inclined to the bar, and which 
are discrete for at least half their length. They are regularly pointed and have feebly 
convex lateral faces and sharp anterior and posterior edges. In outer lateral view 
the whole unit is conspicuously bowed inwards. In aboral view the most conspicuous 
feature is a continuous slit-like groove, which runs to the anterior aboral point of the 
anterior aboral process and along its mid-line, being continued as a narrowing slit 
along the posterior bar. 

The posterior bar is much thinner than the aboral process but the basal groove is 
not conspicuously expanded below the process. It is, however, slightly wider behind 
the posterior part than it is below the anterior. The lateral aboral faces of the aboral 
process are more or less straight in aboral view, the basal margin being widest below 
the posterior end of the process and then curving inward sharply towards the 
posterior bar. The aboral faces are more or less flat. 

Remarks. Collinson & Druce (in press) include this species as a junior synonym 
of N. singularis (Hass). We have only a single specimen in our collections and 
we are not in a position to determine the range of morphological variation. 

Neoprioniodus tulensis (Pander) 
Plate 21, figs. 19a, b 

1856 Prioniodus tulensis Pander (parlim) : 30, PI. 2a, fig. 1 only. 
1928 Prioniodus tulensis Pander ; Holmes (partim) : 22, PI. 3, fig. 18 only. 
1940 Prioniodus cassilaris Branson & Mehl : 186, PI. 6, figs. 11, 12, 15, 17. 
1950 Prioniodus cassilaris Branson & Mehl ; Youngquist, Miller & Downs : 528, PL 67, 
figs. 23, 24. 
non 1957 Prioniodina cassilaris (Branson & Mehl) Bischoff : 47, PI. 5, figs. 38, 39 ( = N. 
peracutus) . 
1963 Neoprioniodus tulensis (Pander) Rexroad & Collinson : 18, PI. 2, fig. 17, 22, 23. 

Material. 5 specimens : figured, X 280. 

Range. North Crop CYD 6-CYD 7. 

Description. The distinctive feature of the present specimens is the long, 
recurved, bluntly pointed anterior denticle, the broad spatulate form of the aboral 
process, and the elongated posterior bar, which bears a series of about 15 denticles 
on its oral surface. These denticles are discrete for most of their length, and decrease 
in size posteriorly. 



BRITISH AVONIAN CONODONT FAUNAS 165 

The anterior denticle is elongated, wide and bluntly pointed. It is gently recurved 
in its distal half, but its proximal half stands only slightly inclined to the anterior 
portion of the posterior bar. It has sharp anterior and posterior edges and very 
feebly convex lateral faces, the outer distal lateral face being almost flat. 

The aboral process is broad in relation to its length. Its anterior edge is a con- 
tinuation of the anterior edge of the anterior denticle, and it is more or less straight. 
Its anterior aboral termination is bluntly rounded and its posterior aboral edge is 
strongly convex. It has flat lateral faces. 

The posterior bar is elongated, and has a concave proximal portion and a relatively 
straight distal portion when seen in outer lateral view. It decreases in depth 
posteriorly and bears about 15 denticles ; those of the median third tend to be the 
largest and they decrease posteriorly in size ; they are basally confluent but are 
discrete for most of their length, with sharp anterior and posterior edges and gently 
convex lateral faces. There is a tendency in the median part of the bar for a 
hindeodellid type of denticulation, but this is not a conspicuous feature of the unit. 
The outer lateral face of the posterior bar is flat and shows a very slight bevelled 
ridge parallel to its aboral surface. The whole unit is gently incurved in a horizontal 
plane, so that its inner lateral face is concave. The denticles of the posterior bar 
stand more or less erect to the bar itself. 

In inner lateral view the anterior denticle is much more strongly curved and the 
curvature is especially strongly developed on the posterior proximal lateral face. 
The inner aboral longitudinal edge of both the aboral process and the posterior bar 
are sharply bevelled and the inner lateral curvature of both the anterior denticle and 
the posterior bar are conspicuous. 

The aboral surface is marked by a shallow pit below the anterior denticle, which is 
extended posteriorly as a very narrow slit-like cavity. The basal cavity also extends 
anteriorly as a narrow slit-like process, running along the median part of the anterior 
aboral surface. The basal cavity itself is not conspicuously laterally expanded. 
There is a strong bevelled flange on the inner aboral edge of the anterior aboral 
process. The strongest lateral curvature of the posterior bar occurs in its anterior 
half, the posterior part being more or less straight. 

Remarks. The only substantial difference between the present species and N. 
scitulus (Branson & Mehl) is the longer posterior bar of the present specimens, which 
bears a greater number of denticles. There seems to be a morphological discon- 
tinuity between the two, but we are not certain about this and further study may 
indicate that the two are morphologically continuous and that N. scitulus should be 
regarded as a junior synonym of N. tulensis. 

Neoprioniodus varians (Branson & Mehl) 
Plate 21, figs. 18a, b 

1940 Prioniodus varians Branson & Mehl : 174, PI. 5, figs. 7, 8. 

1941 Prioniodus barbatus Branson & Mehl ; Ellison & Graves : 3, 4, PI. 1, fig. 27 only. 
1957 Prioniodina varians (Branson & Mehl) Bischofi : 49, PI. 5, fig. 35. 

1957 Prioniodina varians (Branson & Mehl) Ziegler in Fliigel & Ziegler : 50. 



166 BRITISH AVONIAN CONODONT FAUNAS 

1957 Neoprioniodus varians (Branson & Mehl) Rexroad : 35, PI. 2, fig. 10. 

1958 Neoprioniodus varians (Branson & Mehl) Rexroad : 24, PI. 5, figs. 3, 4. 

1961 Neoprioniodus varians (Branson & Mehl) Rexroad & Burton : 1155, PI. 140, figs. 9, 

10. 
1965 Neoprioniodus varians (Branson & Mehl) Rexroad & Nicoll : 24, PI. 2, fig. 18. 

Material. 7 specimens : figured, X 281. 

Range. North Crop CYD 7-3D 17. 

Description. The present specimens have a conspicuous and relatively short 
anterior denticle, which is very wide at its base in comparison with its length. It is 
regularly tapered, its anterior and posterior edges being straight, and its distal tip 
pointed. Its inner lateral face is strongly convex in the proximal portion and less 
strongly convex in the distal portion. It is extended aborally as a very short aboral 
process, with a straight anterior edge and a continuously concave posterior edge, 
which is continuous with the concave margin of the posterior bar when viewed in 
lateral view. Its inner lateral face is only feebly convex, and there is no sharp inner 
basal flexure. 

The posterior bar, when seen in inner lateral view, is continuously and relatively 
strongly curved downward. It decreases in depth posteriorly and its posterior 
aboral corner is bluntly rounded. Its lateral face is strongly convex in the anterior 
half, but flat to feebly convex in the posterior part, its basal margin being slightly 
bevelled. Its oral surface bears about 16 large denticles, between which there are 
some smaller " germ " denticles developed, especially in the anterior third. The 
denticles as a whole are closely crowded, but the major denticles are generally not 
confluent with one another. The denticles in the median half of the bar tend to be 
rather larger in size than the rest. The denticles on the posterior quarter of the bar 
are the smallest. All the denticles stand more or less erect to the basal surface 
below them, and have sharp anterior and posterior edges and convex lateral faces. 
They are short and bluntly pointed. 

The anterior denticle stands erect to the oral surface of the posterior bar in contact 
with it. It is also gently curved inward along its length. 

In outer lateral view, there is a very conspicuous bevelled edge along the whole of 
the aboral margin. The outer lateral face of the anterior denticle and the aboral 
process is more or less flat in the lower proximal portion, but becomes gently convex 
in the distal two-thirds. The curvature of the posterior bar is very conspicuous, and 
the bar decreases in depth posteriorly. In lateral view the anterior end of the aboral 
process is slightly flexed outward in a horizontal plane, and the main part of the 
posterior bar is gently flexed inward, so that its inner lateral face is concave. There 
is a deep and obvious basal cavity below the posterior part of the anterior denticle, 
which decreases in width but is continued as a rather wide extension along both the 
aboral process and the posterior bar. 

Neoprioniodus sp. nov. A 
Plate 22, fig. 14 
Material, i specimen : figured, X 282. 



BRITISH AVONIAN CONODONT FAUNAS 167 

Range. North Crop 3D 17. 

Description. This species is marked by the lack of a large aboral process and 
the presence of a wide flaring basal cavity. The anterior denticle is strongly laterally 
compressed, fairly short and recurved in its aboral third. The posterior bar is deep 
and relatively short, bearing a series of 14 fused, laterally compressed, needle-like 
denticles, which are inclined posteriorly. In aboral view the pit is large and sub- 
apical, having flaring lips. It runs along the posterior bar as a narrowing cavity 
terminating at the posterior extremity of the posterior bar. 

Neoprioniodus cf. armatus (Hinde) 
Plate 21, figs. 3a-c 
1879 Prioniodus armatus Hinde (partim) : 360, PL 15, fig. 20, non fig. 21. 

Material. 3 specimens : figured, X 283. 

Range. North Crop ZLA 14. 

Description. The anterior denticle is tall and laterally compressed. The 
anterior edge is feebly concave in lateral view, with a sharp anterior and posterior 
edge. The blunt aboral surface projects slightly aborally. The posterior bar is 
denticulate, curved inward, and slightly twisted. The fused denticles are small, 
more or less erect, number about 11, and decrease in height posteriorly. The cavity 
is small and situated postero-aborally of the anterior denticle. 

Remarks. This form appears to be very close to Neoprioniodus armatus (Hinde 
1879, PI- z 5> n S- 20 ) which is most abundant in the Upper Devonian. This species 
probably has a long range, and the present specimens may well belong to it but 
because of their limited occurrence, both stratigraphically and numerically, we have 
not made a direct assignation. Hinde's fig. 21 probably represents a different 
species. 

Neoprioniodus cf. camurus Rexroad 
Plate 22, figs. ia-4b 
!957 Neoprionodus camurus Rexroad : 33, PI. 2, figs. 18-20. 
Material. 10 specimens : figured, X 284, X 285, X 286, X 287. 
Range. North Crop 3D 14/15. 

Description. The distinctive features of this species are the relatively elongated 
posterior bar, the sharp inner lateral curvature of the bar immediately posterior to 
the anterior denticle, and the slender anterior denticle and aboral process. 

The posterior bar is more or less straight in inner lateral view, and is relatively 
shallow. Its oral surface bears up to 18 denticles, some of which are separated by 
smaller germ denticles. The denticles are confluent for most of their length, and 
only their apices are discrete. The apices are sharply pointed with sharp anterior 
and posterior edges and gently convex lateral faces ; those in the posterior quarter 



n.S 



BRITISH AVONIAN CONODONT FAUNAS 



stand more or less erect to the basal surface of the bar, but those in the anterior three- 
quarters are inclined slightly anteriorly. The denticles are of variable height but 
there is no conspicuous increase or decrease in height in either direction. There is a 
slight tendency for the two denticles immediately posterior to the anterior denticle to 
be larger than the rest. The anterior denticle, which is not conspicuously large, is 
flexed sharply inwards, so that its inner lateral edge points inwardly and anteriorly, 
making an angle of about 140 ° with the posterior bar. When seen in inner lateral 
view, looking directly at the junction between the anterior denticle and the posterior 
bar, the angle between the posterior edge of the aboral process and the posterior bar 
is about 70 °. The anterior denticle is more or less straight, with sharp and straight 
anterior and posterior edges and gently convex lateral faces. 

The aboral process is relatively short in comparison with the length of the denticles, 
with a rather sharp aboral point, and straight anterior and posterior edges. 

In outer lateral view the most conspicuous feature of the unit is the sharp lateral 
recurvature at a point about two or three denticles posterior to the anterior denticle. 
There is a faintly perceptible longitudinal bevelled edge developed, but the whole 
aboral surface of the unit is rather thin, although it is excavated by a longitudinal 
slit. There is a shallow, little-flared, posterior cavity below the posterior margin of 
the anterior denticle. 

Genus OZARKODINA Branson & Mehl 1933 
1933 Ozarkodina Branson & Mehl 51. 
Type species. Ozarkodina typica Branson & Mehl. 



Ozarkodina curvata Rexroad 
Plate 27, fig. 6 



1958 Ozarkodina curvata Rexroad 
1 96 1 Ozarkodina curvata Rexroad 

1964 Ozarkodina curvata Rexroad 

1965 Ozarkodina curvata Rexroad 
Ozarkodina curvata Rexroad 



24, PI. 4, figs. 1-3. 

Rexroad & Burton : 1156, PI. 141, figs. 13, 14. 
Rexroad & Furnish : 674, PI. in, figs. 10, 11. 
Rexroad & Nicoll : 25, PL 2, figs. 1, 2. 
Collinson & Druce (in press). 



Material, i specimen : figured, X 289. 

Range. North Crop CYD 7. 

Description. The most conspicuous feature of this species is the short, strongly 
depressed anterior bar, which bears a series of about 4 denticles on its oral edge. 
These are basally confluent, and only their apices are discrete, being sharply pointed, 
with gently convex lateral faces. They tend to be recurved parallel to the apical 
denticle, and show a more or less constant decrease in size anteriorly, those adjacent 
to the apical denticle being the largest. The anterior bar is relatively deep and 
relatively straight ; its anterior end is bluntly spatulate and its outer lateral face 
more or less flat. There is a rather flat bevel visible along the whole aboral edge of 
the unit, when seen in outer lateral view. The base of the apical denticle is about 



BRITISH AVONIAN CONODONT FAUNAS 



169 



two to three times as wide as the largest denticles adjacent to it, and is confluent with 
them. It is recurved posteriorly but has a more or less straight posterior edge and is 
bluntly pointed. It has sharp anterior and posterior edges. Its outer lateral face is 
feebly convex, and the basal margin is sharply, but not greatly, outflexed below it to 
give a rather inconspicuous navel. The posterior bar is about twice the length of the 
anterior, but is less deep. It is straight along its aboral margin and the distal end 
makes an angle of about 90 ° with the distal end of the anterior bar. The posterior 
bar decreases in depth posteriorly and bears a series of crowded confluent denticles, 
more or less of similar size. These number up to about 11 or 12, and have rather 
sharply pointed free tips. They show no overall trend in size, but the posterior ones 
tend to be slightly smaller than the rest. Germ denticles are visible between some of 
them. Those near the anterior end of the posterior bar tend to be inclined posteri- 
orly, but those towards the distal end of the bar stand more or less erect to the base 
of the bar itself. The whole posterior bar is sharply inflexed at about its mid-length, 
so that its inner lateral face is longitudinally concave. The posterior aboral corner 
of the unit is sharply rounded. In inner lateral view, the inward curvature of the 
unit is a very conspicuous feature. 

There is a small basal cavity below the posterior edge of the denticle, around which 
the basal margins flare slightly. This is continued as a conspicuous but narrow slit 
along the anterior and posterior bars. 

Ozarkodina cotnpressa Rexroad 
Plate 27, fig. 23 



1957 Ozarkodina compressa Rexroad : 

1958 Ozarkodina compressa Rexroad ; 
1961 Ozarkodina compressa Rexroad ; 

1964 Ozarkodina compressa Rexroad ; 

1965 Ozarkodina compressa Rexroad ; 



36, PI. 2, figs. 1, 2. 

Rexroad : 24, PI. 6, figs. 1, 2. 

Rexroad & Burton : 1156, PI. 141, figs. 16, 17. 

Rexroad & Furnish : 674, PI. in, fig. 9. 

Rexroad & Nicoll : 24, 25, PI. 2, figs. 3, 4. 



Material. 12 specimens : figured, X 420. 

Range. Avon Gorge C 3-S 49, North Crop 3D 14/15-3D 22. 

Description. The present specimens are broadly similar to those described by 
Rexroad and other authors, although they differ slightly in that the posterior bar 



Denticles 



Apical denticle 



Posterior 



Posterior bar 




Anterior 



Anterior bar 



Lip of basal cavity 
Fig. 33. Ozarkodina sp. showing morphological terms used in the text. 



170 BRITISH AVONIAN CONODONT FAUNAS 

tends to be rather more elongate and is slightly twisted. This distinction does not 
seem sufficient, however, to warrant their recognition as a different species, and in 
other aspects of their denticulation and general form they closely resemble Ozarkodina 
compressa. 



Ozarkodina delicatula (Stauffer & Plummer) 
Plate 27, figs. 15, 19 

1932 Bryantodus delicatulus Stauffer & Plummer : 29, PI. 2, fig. 27. 

1932 Bryantodus nasuius Stauffer & Plummer : 29, PI. 2, fig. 28. 

1932 Bryantodus sulcatus Stauffer & Plummer : 30, PI. 2, figs. 11, 14, 30. 

1933 Bryantodus delicatus Gunnell : 267, PI. 32, fig. 43. 
1933 Bryantodus rugosus Gunnell : 269, PI. 32, fig. 44. 
1933 Bryantodus stritatus Gunnell : 268, PI. 32, fig. 45. 
1933 Bryantodus strigillatus Gunnell : 268, PI. 32, fig. 46. 

non 1933 Bryantodus delicatus (Stauffer & Plummer) Branson & Mehl : 222, PI. 16, fig. 19. 
1941 Ozarkodina delicatula (Stauffer & Plummer) Ellison : 120, PI. 20, figs. 40-42, 47. 
1 94 1 Ozarkodina delicatula (Stauffer & Plummer) Ellison & Graves : 3, PI. 1, figs. 

12-14. 
1944 Ozarkodina delicatula (Stauffer & Plummer) E. B. Branson : 327. 

1948 Ozarkodina delicatula (Stauffer & Plummer) Youngquist & Heezen : 771, PI. 118, 
fig. 6. 

1949 Ozarkodina delicatula (Stauffer & Plummer) Youngquist & Downs : 168, PI. 30, 
figs. 1, 3, 7, 11. 

non 1949 Bryantodus delicatus (Stauffer & Plummer) Beckmann 161, PI. 1, fig. 7 ; PI. 3, 

fig- 3- 
1952 Ozarkodina delicatula (Stauffer & Plummer) Rhodes : 893, PI. 126, figs. 2, 3. 

1957 Ozarkodina delicatula (Stauffer & Plummer) Bischoff : 39, PI. 1, figs. 25-28. 

1958 Ozarkodina compressa Rexroad (partim) : 24. 

1961 Ozarkodina delicatula (Stauffer & Plummer) Higgins : 220, PI. 12, fig. 13. 

1961 Ozarkodina delicatula (Stauffer & Plummer) Rexroad & Burton : 1156, PI. 141, 

fig. 12. 
1963 Ozarkodina delicatula (Stauffer & Plummer) Bouckaert & Higgins : 17, fig. 3. 

Ozarkodina delicutula (Stauffer & Plummer) Collinson & Druce (in press). 

Material. 27 specimens : figured, X 290, X 291. 
Range. North Crop CYD 7-3D 20. 

Description. This is a relatively variable species with the following character- 
istics. Anterior and posterior bars are thin, blade-like, straight or continuously 
gently arched, the anterior tending to be the deeper and the longer. Denticles 
closely spaced, more or less sub-equal, discrete only at their pointed apical ends. 
Apical denticle is from one and a half to three times the width of the adjacent 
denticles. It has a slightly flared basal cavity. 

The anterior bar is of more or less uniform depth and has a straight to gently 
concave aboral edge. It bears 12 to 14, strongly laterally compressed denticles, 
which are confluent for most of their length only their apical tips being discrete. 
These are sharply pointed, with sharp anterior and posterior edges which are straight. 
The anterior bar itself is about equal in depth to the length of the denticles. The 



BRITISH AVONIAN CONODONT FAUNAS 171 

denticles at the anterior end of the bar are more or less erect, but those toward the 
posterior end become increasingly strongly inclined posteriorly. In a few specimens 
the denticles at the anterior end of the bar are also posteriorly inclined. The lateral 
faces of the anterior bar are flat to gently convex, the convexity increasing in the 
posterior half of the bar. The apical denticle is variable in size and in inclination. 
It is of similar form to the denticles of the anterior bar and its free portion is sharply 
pointed, with sharp, straight anterior and posterior edges. It is strongly inclined at 
an angle of up to about 50° to the posterior bar, and is from one and a half to three 
times as wide and about twice as long as the largest adjacent denticles. In some 
specimens the denticles of the anterior bar are more widely spaced and appear almost 
discrete, but in most specimens they are more or less confluent. 

The posterior bar is depressed with respect to the anterior, and the whole aboral 
surface is either continuously and gently concave, or both the anterior and posterior 
bars may be more or less straight and meet at an angle of about 120 °. (This is the 
projected angle made by their straight distal ends in those specimens where the lower 
surface is strongly arched). The posterior bar bears 10 or more laterally compressed 
closely spaced denticles, which, although in some specimens they are more or less 
equal in size, show a marked decrease in size in the posterior quarter of the bar in 
others. They are generally rather smaller than the denticles of the anterior bar and 
fewer in number. In some specimens the posterior bar, and to a lesser extent the 
anterior bar, are strongly flexed inwards. The denticles of the posterior bar are all 
inclined at about 50 ° to the posterior bar itself. 

In aboral view the unit has a rather conspicuously flattened aboral margin, which 
decreases in width towards the anterior and posterior ends of the unit. There is a 
continuous longitudinal slit along both limbs, and a slightly flared median cavity 
below the apical denticle, which is continuous with the slit. The flaring of this cavity 
is not a conspicuous feature, but the thickened lips of the main longitudinal cavity 
are more or less conspicuous in aboral view. 

This species shows some variation in the degree of flexing of the anterior and 
posterior bars in a vertical plane and in the relative depth and detailed denticulation 
of the anterior bar. Specimens illustrating various morphological variations are 
illustrated. 

Ozarkodina hindei Clarke 
Plate, 27 figs. 16, 17, 22 

1879 Polygnathus dubius Hinde : 363, PI. 16, fig. 8 only. 

1900 Polygnathus dubius Hinde ; Hinde : 341, PI. 9, fig. 1 only. 

1928 Prioniodina (Polygnathus) dubius (Hinde) Holmes : 19, PI. 8, fig. 1 only. 

i960 Ozarkodina hindei Clarke : 18, PI. 3, figs, i, 6. 

1961 Ozarkodina compressa Rexroad ; Rexroad & Burton : PI. 141, fig. 16 only. 

Material. 3 specimens : figured, X 294, X 293, X 295. 

Range. North Crop 3D 6-3D 12. 

Description. The diagnostic features of this species are the very deep and 
strongly laterally compressed anterior and posterior bars, and the very wide, short 



172 BRITISH AVON1AN CONODONT FAUNAS 

and conspicuously pointed apical denticle. The anterior bar is deeper than the 
posterior, and carries from 4 to 6 denticles on its oral edge. These are very strongly 
laterally compressed and more or less sharply recurved, being confluent for the 
greater part of their length. Their apical halves are discrete, and they are sharply 
pointed with straight anterior and posterior edges, the anterior edge tending to be 
sharply deflected at an angle of about 130 ° at or near the point of confluence with the 
adjacent denticles, but the posterior edge being straight throughout its length. 
Germ denticles are visible in places on the anterior bar, especially at its junction 
with the apical denticle. The most posterior denticle of the apical bar is so coalesced 
with the anterior edge of the apical denticle that only its highest portion is discrete. 
The anterior bar tends to show a slight increase in depth anteriorly ; the denticles in 
the posterior two thirds of the bar are of more or less uniform height. There may, 
however, be 1 or 2 much smaller blunt denticles present on the spatulate anterior end. 
The denticles may curve slightly inwardly in some specimens. The inner lateral face 
of the anterior bar is more or less flat, but the outer lateral face has a conspicuous, 
shoulder-like thickening near the base of the denticles. The anterior bar tapers 
sharply towards the aboral margin. 

The apical denticle is at least three times as wide as the largest denticles of the 
anterior and posterior bars. It is very sharply pointed, and is only about twice as 
long as its basal width. It is recurved posteriorly at an angle of about 60 ° to the 
posterior bar, and germ denticles are conspicuous at its base. There is a feebly 
flaring protrusion of the basal margin below its posterior margin. 

The posterior bar is shorter and shallower than the anterior, and bears up to 9 
denticles of more or less uniform height, basally confluent, but their apices discrete 
and sharply pointed. They tend to be very slightly smaller than those of the larger 
series of the anterior bar. The posterior bar thickens towards its aboral surface, 
which is wide and flat, as an extension of the basal cavity below the apical denticle. 
It decreases in both width and depth posteriorly, however, and its posterior aboral 
margin is bluntly rounded. Its inner lateral face is more or less flat and the posterior 
denticles are gently inclined to the base of the posterior bar. The posterior bar and 
the anterior bar have relatively straight aboral margins and they make an angle of 
about 130 ° with one another in a vertical plane. 

The whole unit is strongly bowed laterally in a horizontal plane so that it is concave 
on the inner side, and the denticles are also incurved to a varying degree. This is 
especially true of the apical denticle. The anterior edge of the anterior bar has an 
acute angle at the anterior aboral margin and is inclined sharply posteriorly, with a 
faintly serrated anterior edge in some specimens. In outer lateral view the lateral 
faces of the unit are flat to gently convex, and the inner curvature is a conspicuous 
feature. In most specimens there is developed to a varying intensity a bevelled 
aboral margin, especially conspicuous in the median half of the unit, which includes 
the posterior part of the anterior bar and the anterior part of the posterior bar. The 
outer lateral view of the navel below the posterior edge of the apical denticle is 
distinct and forms a rather flattened apical area. 

In aboral and outer lateral views the basal cavity is a conspicuous feature, partic- 



BRITISH AVONIAN CONODONT FAUNAS 173 

ularly so in outer view. There is a strong basal expansion below the posterior edge 
of the apical denticle, and in the anterior third of this, the basal cavity is deepest and 
widest, forming a biconvex pit. It is extended anteriorly and posteriorly as a shallow 
slit-like groove, but the posterior extension becomes indistinct near the posterior end 
of the margin of the expanded base. The anterior extension continues towards but 
does not quite reach the anterior end of the anterior blade. 

Remarks. This species is close to 0. compressa Rexroad, but differs from it in the 
shorter and deeper anterior and posterior bars and the short and relatively very 
broad apical denticle. 

Ozarkodina macer (Branson & Mehl) 

Plate 27, figs. 7, 8 

1934 Bryantodus macer Branson & Mehl : 283, PI. 23, fig. 4. 

1934 Ozarkodina elongata E. R. Branson : 313, PI. 28, fig. 25. 

? 1934 Bryantodus scitulus Branson & Mehl : 283, PI. 23, fig. 5. 

1943 Bryantodus equalis Cooper in Cooper & Sloss : 170, PI. 29, fig. 9. 

1943 Bryantodus cf. planus Branson & Mehl ; Cooper in Cooper & Sloss : 170, PI. 29, 

fig- 3- 
1943 Ozarkodina regularis Branson & Mehl ; Cooper in Cooper & Sloss : 170, PI. 29, fig. 12. 
1943 Subbryantodus grandis Cooper in Cooper & Sloss : 175, PL 29, fig. 19. 
1949 Ozarkodina cf. elongata Branson & Mehl ; Thomas : 411, PI. 4, fig. 28. 
1955 Ozarkodina regularis Branson & Mehl ; Sannemann : 133, PI. 6, fig. 5 only. 
1957 Ozarkodina willsi Rhodes & Dineley : 364, PI. 38, figs. 1, 5. 
1957 Ozarkodina firma (Stauffer) Rhodes & Dineley : 364, PI. 27, fig. 20. 
1957 Ozarkodina delicatula (Stauffer & Plummer) Bischoff : 39, PI. 1, figs. 25-28. 
1957 Ozarkodina roundyi (Hass) Bischoff : 40, PI. 2, fig. 2 only. 

1957 Ozarkodina congesta Stauffer, Bischoff & Ziegler : 75, 76, PI. 12, figs. 18-20, PI. 13, 
fig. 14. 

1958 Ozarkodina tortilis Tatge ; Huckriede : 154, PI. n, fig. 26 only. 

!959 Ozarkodina cf. delicatula (Stauffer & Plummer) Helms : 646, PI. VI, figs. 14-16. 
x 959 Ozarkodina cf. regularis Branson & Mehl ; Helms : 647, PL IV, figs. 13, 14, (non PL 

IV, fig. 15 = 0. cf. congesta). 
i960 Ozarkodina regularis Branson & Mehl ; Zimmermann : PL IX, fig. 11 only. 
i960 Ozarkodina media Walliser ; Spasov : 68, PL 1, fig. 10 only. 

Material. 71 specimens : figured, X 304, X 305. 

Range. Avon Gorge K 8-Z 38. 

Description. A gently arched blade with asymmetrical anterior and posterior 
blades, commonly bearing 5 to 7 straight, posteriorly inclined denticles on the 
anterior blade, and 8 to 12 straight posteriorly inclined denticles on the posterior 
blade. The denticles of the anterior and posterior blades may be of uniform eleva- 
tion, highest near the apical denticle and decreasing in elevation to the extremities of 
the blades, or they may be of variable elevation. The apical denticle is straight to 
slightly curved, posteriorly inclined and higher and wider than the blade denticles. 
The small circular basal cavity is situated beneath the apical denticle. The aboral 
edge is sharp. 



174 BRITISH AVONIAN CONODONT FAUNAS 

Remarks. Ozarkodina macer (Branson & Mehl) as here denned, includes a group 
of ozarkodinids which are characterized by having asymmetrical anterior and 
posterior limbs. The outline of the denticles of both the anterior and posterior 
blades is similar in lateral view. 0. macer resembles 0. cf. congesta in the outline of 
the blades in lateral view, but in 0. macer the anterior and posterior limbs are 
asymmetrical whereas in 0. cf. congesta they are symmetrical. 

Compared with Ozarkodina macra the blade of Ozarkodina macer is thinner. 

Ozarkodina macra Branson & Mehl 
Plate 27, figs. 12, 20, 21 

? 193 1 Bryantodus equalis Cooper : 234, PI. 28, fig. 9. 

? 1931 Bryantodus subequalis Cooper : 234, PI. 28, fig. 11. 

1934 Ozarkodina macra Branson & Mehl : 192, PI. 17, fig. 5. 

1934 Ozarkodina regularis Branson & Mehl : 287, PI. 23, figs. 13, 14. 
? 1938 Ctenognathus firmus Stauffer : 425, PI. 48, figs. 2, 6, 15. 

1955 Ozarkodina regularis Branson & Mehl ; Sannemann : 133, PI. 6, figs. 3, 7 only. 
? 1956 Ozarkodina rhenana Bischoff & Ziegler : 153, PI. 14, fig. 19. 
? 1957 Ozarkodina ballai Bischoff & Ziegler : 74-75, PI. 13, figs. 1, 2. 

1957 Ozarkodina macra Branson & Mehl ; Bischoff & Ziegler : 77, PI. 12, figs. 13a, b, PI. 13, 
figs. 10a, b. 

1957 Ozarkodina cf. macra Branson & Mehl ; Bischoff & Ziegler : 78, PI. 13, fig. 11, PI. 19, 
fi g- 43 

Material. 36 specimens : figured, X 296, X 298, X 297. 

Range. Avon Gorge K 2-Z 18, North Crop KL 2-KL 16. 

Description. The aboral edge in lateral view is slightly arched. The anterior 
and posterior blades are of almost equal length, and bear 8-12 straight, posteriorly 
inclined denticles, fused for the greater part of their length but free at their tips. The 
anterior blade is thicker than the posterior blade. The apical denticle is two to three 
times as wide as the denticles of the anterior and posterior blade. It is inclined to the 
posterior at an angle of 70 °. The small circular basal cavity is situated immediately 
beneath the apical denticle and the aboral edge is sharp. 

Ozarkodina parva (Huddle) 
Plate 27, fig. 18 

1934 Bryantodus parvus Huddle : 74, 75, PI. 4, fig. 9. 

1939 Bryantodus orthus Cooper : 385, PI. 43, figs. 33, 34. 

J 939 Subbryantodus ? scitulus (Branson & Mehl) Cooper : 417, PI. 43, figs. 35, 36. 

Material. 107 specimens : figured, X 299. 

Range. Avon Gorge K 3-C 7, North Crop KL 2-ZLA 32. 

Description. The blade is short, thin, symmetrical and slightly arched. The 
apical denticle is subcentral, flattened, sharp edged and acutely pointed to the poster- 
ior. The blade denticles are closely appressed and similar to the apical denticle in 
outline, inclination and insertion. They number 7 to 12 on each side of the apical 



BRITISH AVONIAN CONODONT FAUNAS 175 

denticle, are fused for the greater part of their length, and are highest near the apical 
denticle. They decrease in height uniformly to the anterior and posterior extremi- 
ties. The basal cavity is small and thin, and is situated beneath the apical denticle. 

Ozarkodina plana (Huddle) 
Plate 27, figs. 1-3 

1934 Bryantodus planus Huddle : 75-76, PI. 10, fig. 8. 

non 1934 Bryantodus planus Huddle ; Branson & Mehl : 284, PI. 23, fig. 8. 

1957 Ozarkodina cf. O. plana (Huddle) Rhodes & Dineley : 364, PI. 37, fig. 24. 

1961 Ozarkodina plana (Huddle) Scott & Collinson : 128, PI. 2, fig. 8. 

Material. 12 specimens : figured, X 300, X 301, X 419. 

Range. Avon Gorge K 3-Z 15. 

Description. The anterior and posterior blades are short, slightly arched, 
laterally compressed, and very thin. The apical denticle is short, broad at the base, 
acutely pointed and situated slightly anterior to the basal cavity. The blade 
denticles are similar in outline to the apical denticle and usually number 4 anteriorly 
and 6 posteriorly. The basal cavity is small and situated slightly anterior to the 
apical denticle. 

Ozarkodina plumula Collinson & Druce 
Plate 27, figs. 4, 5 

Ozarkodina plumula Collinson & Druce (in press). 
Material. 4 specimens : figured, X 302, X 303. 
Range. North Crop 3D 12. 

Description. The diagnostic characteristic of this species is the slender elon- 
gated anterior bar, bearing a large number of small, posteriorly inclined denticles. 
The posterior bar is shorter and deeper, and bears a smaller number of conspicuously 
larger denticles than those of the anterior bar. The apical denticle is only slightly 
larger than the largest of the posterior bar and the whole unit is more or less con- 
tinuously recurved. The anterior bar is of slender elongate construction, relatively 
shallow in depth, and bears a series of up to 12 small confluent denticles, only the 
apical tips of which are discrete. These are sharply inclined to the anterior bar and 
tend to decrease in size posteriorly. 

The apical denticle is only slightly larger than those adjacent to it both in length 
and in width. It is, however, conspicuously more sharply inclined than most of 
those of the anterior bar, and in this it parallels the denticles of the shorter posterior 
bar. It is very strongly laterally compressed, with sharp anterior and posterior 
edges, and is confluent with the posterior denticles for the greater part of its posterior 
margin, though its inclination removes most of its anterior edge on the adjacent 
anterior denticles. 

The denticles of the posterior bar are similar to, but rather larger than, those of the 



176 BRITISH AVONIAN CONODONT FAUNAS 

anterior. They are about 5 or 6 in number and are strongly laterally compressed 
with sharp anterior and posterior edges and gently biconvex lateral faces. Their 
bases are confluent and their sharply pointed apices discrete. The posterior bar is 
deeper than the anterior, and tends to become shallower towards its posterior end. 
It is inclined to the anterior bar at an angle which varies from I30°-I40°, although 
the junction between the two is continuously curved, so that the whole aboral 
margin is concave with more or less straight distal ends. 

There is a relatively inconspicuous flare on the basal margin below the posterior 
edge of the apical denticle. The basal cavity is gently flared, being slightly larger 
than that of many typical ozarkodinids. It is continued as a longitudinal slit along 
both the anterior and the posterior bars, both of which become narrower towards the 
aboral margin. The whole unit is more or less straight in a vertical plane. 

In complete specimens the denticles are seen to be sharply pointed, and the 
denticles of the posterior bar are discrete for a greater part of their length than those 
of the anterior bar. The posterior aboral corner of the posterior bar is very strongly 
rounded and terminates orally in the tip of the posterior denticle. 



Ozarkodina cf. congesta Stauffer 

Plate 27, fig. 13 

1940 Ozarkodina congesta Stauffer : 427, PI. 59, fig. 12. 

1957 Ozarkodina plana Huddle ; Bischoff & Ziegler 78, 79, PI. 12, fig. 15a, b. 

1959 Ozarkodina cf. regularis Branson & Mehl ; Helms : 647, PI. IV, fig. 15 only. 

Material. 14 specimens : figured, X 288. 

Range. Avon Gorge Z 17-Z 37. 

Description. A gently arched unit with symmetrical anterior and posterior 
blades, commonly bearing 7 straight posteriorly inclined denticles, highest near the 
apical denticle, and decreasing in length uniformly to the anterior and posterior 
extremities of the blades. The apical denticle is straight to slightly curved, 
posteriorly inclined and higher and wider than the blade denticles. The small 
circular basal cavity is situated beneath the apical denticle, The aboral edge is 
sharp. 

Remarks. In the Z beds of the Avon Gorge, specimens of Ozarkodina are found, 
which are neither identical with one another nor with previously described species. 
Reference to the literature shows that previous workers, for example Helms (1959) 
and Bischoff & Ziegler (1957), have often assigned specimens in their studies to 
species where the holotype bears little resemblance to their specimens. In the 
present study, the majority of the Z bed ozarkodinids have been referred to two 
general categories ; 0. cf. congesta Stauffer, which has symmetrical anterior and 
posterior limbs, and Ozarkodina macer (Branson & Mehl) which has asymmetrical 
anterior and posterior limbs. 



BRITISH AVONIAN CONODONT FAUNAS 177 

Ozarkodina cf. delicatula (Stauffer & Plummer) 
Plate 27, fig. 14 

1932 Bryantodus delicatula Stauffer & Plummer 29, PI. 2, fig. 27. 

Material. 12 specimens : figured, X 292. 

Range. North Crop ZLA 31-ZLA 33. 

Description. The unit is bowed and slightly curved. Both bars are long. The 
anterior bar bears about 8 denticles which are sub-equal, laterally compressed, fused 
at their bases with free chevron tips, and all are inclined posteriorly. The antero- 
aboral edge is bluntly spatulate. The apical denticle is largest, fairly short, about 
twice the size of those of the anterior bar, laterally compressed and inclined 
posteriorly. The posterior bar is of equal length to the anterior bar, but less deep, 
and shallows posteriorly. The denticles are similar and about 8 in number. The 
basal cavity is minute and restricted to the aboral region of the apical denticle with 
sometimes feebly flaring lips. 

Remarks. Stauffer & Plummer (1932 : 29), described 0. delicatula from Penn- 
sylvanian strata, and it has been recognized in Upper Visean and Namurian rocks 
(Bischoff 1957, Higgins 1961). The present specimens appear to be very similar to 
the type specimens, and it is possible that the species has an even longer range than 
previously thought. 

Ozarkodina cf. elegans (Stauffer) 

Plate 27, fig. 24 

1938 Ctenognathus elegans Stauffer : 425, PI. 48, figs. 9, 12. 

1940 Ctenognathus elegans Stauffer ; Stauffer : 422, PI. 59, figs. 3-5, 8. 

1955 Ozarkodina elegans (Stauffer) Sannemann : 133, PI. 6, fig. 9. 

1956 Ozarkodina denckmanni Ziegler : PI. 7, figs. 1, 2, PI. 6, figs. 30, 31. 

1957 Ozarkodina elegans (Stauffer) Bischoff & Ziegler : 76, PI. 20, figs. 29-33. 

1958 Ozarkodina denckmanni Ziegler ; Bischoff & Sannemann : 99, PI. 14, figs. 22, 23. 
i960 Ozarkodina regularis Branson & Mehl ; Zimmermann : PI. IX, fig. 10. 

1961 Ozarkodina delicatula (Stauffer & Plummer) Rexroad & Burton : 1156, PI. 141, 

fig. 12. 
1963 Ozarkodina media Walliser ; Spasov & Veselinovic : 246, PI. 1, fig. 14 only. 

Material. 2 specimens : figured, X 109. 

Range. Avon Gorge Z 19-Z 37. 

Description. The anterior blade bears 11 denticles fused to near their tips. The 
denticles are straight and inclined to the posterior at an angle of 80 °. The posterior 
blade is straight and only half the height of the anterior blade. It bears up to 12 
denticles, which are fused for the greater part of their length, but free at their tips. 
The denticles of the posterior blade are free for a greater part of their length than 
those of the anterior blade. The denticles of the posterior blade are straight and 
inclined to the posterior at an angle of 45°. The aboral edge in lateral view, is 
gently arched. The apical denticle is straight, slightly higher than the posterior 



178 BRITISH AVONIAN CONODONT FAUNAS 

denticle of the anterior blade, and inclined to the posterior at an angle of 70 °. It is 
also three times the width of the blade denticles. The small circular basal cavity is 
situated beneath the apical denticle. The aboral edge is sharp. 

Remarks. Ozarkodina cf. elegans, as interpreted in this study, is characterized by 
having longer denticles on the anterior blade than on the posterior blade. 

Ozarkodina sp. 
Plate 27, figs. 9-11 

Material. 93 specimens : figured, X 306, X 307, X 308. 

Range. Avon Gorge K 2-S 53. 

Remarks. A number of broken specimens which contain part of the anterior, or 
posterior blades, have been found, but it is impossible to refer them to any species 
with certainty. 

Genus PATROGNATHUS gen. nov. 

Derivation of name. From the Latin pater — father. 

Diagnosis. Symmetrical platform conodonts, with lanceolate platform and 
short anterior median blade, generally of five denticles, the most posterior one of 
which is higher than the others. The platform bears a row of 6 to 9 nodes on either 
margin, separated by a central trough. The basal cavity is large, extending almost 
the complete length of the aboral surface of the platform, asymmetrical and laterally 
flared. A small posterior blade, composed of two denticles, is developed in a few 
specimens, but there is no carina extending along the platform. 

Type species. Patrognathus variabilis gen. et. sp. nov. 

Description. As for Patrognathus variabilis sp. nov. 

Remarks. Patrognathus is similar to the previously described genera Taphro- 
gnathus Branson & Mehl, and Streptognathodus Stauffer & Plummer, but has a wider 
and more flared basal cavity. Rexroad (1958A) considered Taphrognathus and 
Streptognathodus to be homoeomorphs, but Lindstrom (1964 : 173) considered Taphro- 
gnathus to be a synonym of Streptognathodus. The present authors believe Rexroad's 
interpretation to be correct, and regard Patrognathus as another broad homoeomorph, 
which is present at the base of the Tournaisian and possibly in the uppermost Upper 
Devonian. 

Glenister & Crespin (1959) reported Taphrognathus from the Upper Devonian strata 
of the Fitzroy Basin in Australia. The specimens have an anterior blade which is 
lateral in position and, therefore, appear referable to our new genus Clydagnathus. 
Likewise Conil, Lys & Mauvier (1964) reported, but did not illustrate, Taphrognathus 
sp. from the Tni b -Tn2b horizons of the Franco-Belgian Province. If the anterior 
blade is lateral in position, then their specimens should be referred to Clydagnathus 
gen. nov. Glenister & Klapper (1966, PI. 94, fig. 3) have found specimens of 
" Scaphignathus " in Australia identical to our Clydagnathus. In one sample it 



BRITISH AVONIAN CONODONT FAUNAS 



179 



occurs 150 ft. below the first appearance of 5. aculeatus, but in another it occurs 
with S. aculeatus and Palmatolepis glabra. Sandberg & Klapper (1967) have also 
found the genus Clydagnathus in several sections in Wyoming and Montana, and the 
genus Patrognathus in the Windy Gap Formation of Wyoming, where it is associated 
with S. sulcatus (see also p. 54) 

The Lower Devonian Eognathodus Philip differs from Patrognathus in the form of 
the anterior blade, although the genera resemble one another in overall form. 

Patrognathus variabilis gen. et sp. nov. 
Plate 2, figs. 8a-nc 

Derivation of name. From the great variability of this form. 

Diagnosis. Elongate, symmetrical form, possessing lanceolate platform and 
medial blade. Carina absent. Posterior denticle of blade twice as large as other 
blade denticles. Cavity flared, elongate, covering most of platform. Base of 
cavity and blade grooved. 

Material. 625 specimens : Holotype X 311, Paratypes X 519, X 309, X 310 
(all figured). 

Type locality and horizon. Avon Gorge, K Zone. Sample KL2. 

Range. Avon Gorge Samples K i-K 17, North Crop Samples KL i-KL 12. 

Description. The unit is symmetrical, the platform being lanceolate and 
straight to slightly curved. The blade varies in length, but is commonly a little 



A Orol view 

High denticle of blade 

Blade 



Anterior 




Platform 

Posterior 

Platform denticle 



Position of basal cavity 



B. Aboral view 



High denticle of blade 




Anterior edge 
Flared basol cavity 



Anterior edge 




High denticle of blade 
.^Orol edge 

Posterior edge 



Aboral edge 



Position ot basal cavity 
C. Lateral view 



Fig. 34. Patrognathus sp. showing morphological terms used in the text. 



i8o 



BRITISH AVONIAN CONODONT FAUNAS 



shorter than the platform. It is situated medially and bears from 4 to 8 denticles, 
the posterior-most being twice as large as the remainder. There is a general decrease 
in size anteriorly, and the denticles are more or less erect. The base of the blade is 
grooved. 

Each side of the platform bears a marginal row of laterally elongate nodes, which 
are transversely paired. These are replaced posteriorly by a single series of medial 
transverse ridges, composed of two nodes. An additional node is generally 
developed on the left side of the platform (viewed from the posterior). This addi- 
tional node, situated at the anterior end of the platform, is developed on the left 
margin of the platform, irrespective of whether the unit is laterally curved to the 
right or the left. The number of nodes in each row ranges from 4 to 11. The unit is 
arched slightly in lateral view and the platform has a nodose edge. 

In aboral view the cavity is slightly asymmetrically expanded, the inner half being 
shorter and more inflated. The base of the cavity is grooved. 

Remarks. Although P. variabilis possesses a variable number of nodes on both 
the blade and platform, calculations of denticle density of both blade and platform 
and the construction of a scatter diagram of this information, suggest that this vari- 
tion is continuous (see Fig. 35). The additional node at the anterior of the inner row 
of lateral nodes on " right " specimens appears to be constant and implies that 
paired members of P. variabilis were not symmetrical. Other examples of this 
asymmetry are to be seen in the genera Cavusgnathus, Scaphignathus, Mestognathus 
and Pseudopolygnathus. 



SCATTER DIAGRAM TOR DENTICLE DENSITY 
OF PATROGNATHUS VARIABLIS. 



♦ O CD 



-KL2 22 PLOTS 
>«KL3 54PLOTS 



15 20 30 

platform denticle density 

blade denticle density • no of blade oenticles 
length or blade in mm 

platform denticle densityb No of platform denticles 
length of platform in mm 



Fig. 35. Scatter diagram to show the relationship between the density of denticles on the 
blade and those on the platform of the species Patrognathus variabilis. 



BRITISH AVONIAN CONODONT FAUNAS 181 

Genus PLECTOSPATHODUS Branson & Mehl 1933 

1933 Plectospathodus Branson & Mehl : 47. 
Type species. Plectospathodus flexuosus Branson & Mehl. 

Plectospathodus ? sp. nov. A 
Plate 25, figs. 8a-9 

Material. 3 specimens : figured, X 312, X 313. 
Range. North Crop ZLA 33. 

Description. A plectospathodid characterized by a long anterior bar ; denticles 
free standing, sub-circular in cross-section and posteriorly inclined ; those in the 
median third the largest. Apical denticle larger than bar denticles, ovate in cross- 
section, and posteriorly and laterally inclined. Posterior bar about equal in length 
to anterior bar, twisted and with slight inward curvature, the posterior tip down- 
flexed. Denticles small, fine, except for terminal denticle, which is as large as apical 
denticle, and may have small denticles developed on its posterior face. 

The basal cavity is open, flared on the inner side, with a " nick " in the inner lip 
beneath the apical denticle ; it extends beneath the posterior and anterior bars for a 
short distance. 

Remarks. The genus Plectospathodus has previously been described only from 
rocks of Upper Silurian and Lower Devonian age, but these specimens agree perfectly 
with the generic description given by Branson & Mehl (1933 A : 47). 

Plectospathodus ? sp. nov. B 
Plate 25, figs. 10-12 

Material. 4 specimens : figured, X 427, X 428, X 314. 

Range. North Crop 3D 14/15-3D 19. 

Description. Very small units consisting of two bars, roundly arched at their 
junction. Oral edges denticulate. A conspicuous apical denticle. Denticles of 



Apical denticle 




Terminal denticle 



Posterior bar 



Fig. 36. Plectospathodus sp. showing morphological terms used in the text. 



182 BRITISH AVONIAN CONODONT FAUNAS 

variable size, inclined posteriorly ; at or near posterior end of unit a relatively 
enormous, greatly elongated denticle, slightly greater in basal width than apical 
denticle. 

The inner lateral face is generally convex, with a rather flat oral shoulder on which 
the denticles are developed. The denticulation of the anterior bar consists of a 
series of rather small inconspicuous basally confluent denticles, all inclined equally 
posteriorly at an angle of about 45 ° to the oral edge of the bar. The anterior end is 
roundly spatulate and there is a very feeble basal flare below the apical denticle. 
The apical denticle is biconvex in cross-section, with blunt anterior and posterior 
edges, and is curved slightly inward, as well as being inclined posteriorly. On the 
posterior bar there is a series of denticles which decrease in size towards the distal 
end ; they are basally confluent and have sharp free tips, the most posterior, or the 
one next to it, being much the largest. The posterior portion of the posterior bar is 
straight-edged, but the posterior aboral corner is bluntly rounded. The whole aboral 
surface of the unit is gently concave in lateral view and the unit tends to be bowed 
inwards, as well as the main denticles being rather incurved. In outer lateral view 
the whole unit is rather flat and is slightly indented below the apical denticle. The 
basal surface is flared on the inner lateral face below the apical denticle, and there is a 
broad cavity in this position, which rapidly decreases anteriorly and posteriorly, to 
be extended along part of both bars as a shallow longitudinal slit. 

Genus POLYGNATHUS Hinde 1879 
1879 Polygnathus Hinde : 359. 
Type species. Polygnathus dubia Hinde 1879. 

Polygnathus communis communis Branson & Mehl 
Plate 12, figs. 2a-5c 

1934 Polygnathus communis Branson & Mehl : 293, PI. 24, figs. 1-4. 

1934 Polygnathus communis Branson & Mehl ; E. R. Branson : 308, PI. 25, figs. 5, 6. 

1938 Polygnathus communis Branson & Mehl ; Branson & Mehl : 145, PI. 34, figs. 39-41. 

1939 Polygnathus communis Branson & Mehl ; Cooper : 399, PI. 39, figs. 1, 2, 9, 10, 23, 24. 
1939 Polygnathus adola Cooper : 399, PI. 39, figs. 33-36. 

x 939 Polygnathus marginata Branson & Mehl ; Cooper : 401, PI. 41, figs. 15, 16. 

1944 Polygnathus communis Branson & Mehl ; Branson & Mehl in Shimer & Schrock : 245, 

PI. 94, figs. 29-31. 
1944 Polygnathus communis Branson & Mehl ; E. B. Branson : 208, 221, PI. 39, figs. 39-41. 
1947 Polygnathus communis Branson & Mehl ; Mehl & Thomas : 15, PI. 1, fig. 36. 
1949 Polygnathus communis Branson & Mehl ; Youngquist & Patterson : 62, PI. 15, figs. 

7.8. 
1949 Polygnathus communis Branson & Mehl ; Thomas : 411, PI. 3, fig. 70. 
1951 Polygnathus communis Branson & Mehl ; Youngquist & Downs : 787, PI. in, figs. 

4, 5, 19, 20. 
1951 Polygnathus communis Branson & Mehl ; Hass : 2538, 2539, PI. 1, fig. 10. 
1956 Polygnathus communis Branson & Mehl ; Bichoff & Ziegler : 156, PI. 12, figs. 1-3. 
1956 Polygnathus communis Branson & Mehl ; Hass : 24, 25, PI. 2, figs. 3-5. 



BRITISH AVONIAN CONODONT FAUNAS 183 

1957 Polygnathus communis Branson & Mehl ; Bischoff : 42, PI. 2, figs. 23-27. 

1957 Polygnathus communis Branson & Mehl ; Ziegler in Fliigel & Ziegler : 46, PI. 2, 

fig- 15- 
!959 Polygnathus communis Branson & Mehl ; Hass : 390, PI. 49, figs. 9-11, 13. 
1959 Polygnathus communis Branson & Mehl ; Helms : PI. 3, fig. 11. 
J 959 Polygnathus communis Branson & Mehl ; Voges : 288, PI. 34, figs. 1-7. 
i960 Polygnathus communis Branson & Mehl ; Ziegler : PI. 1, fig. 9. 
i960 Polygnathus communis Branson & Mehl ; Dvorak & Freyer : 884-888, PI. 1, figs. 15, 

16. 
i960 Polygnathus decorosa Stauffer ; Dvorak & Freyer : 882, PI. 2, figs. 1-2. 
1961 Polygnathus communis Branson & Mehl ; Beach : 49, PI. 6, figs. 1-4. 
1961 Polygnathus communis Branson & Mehl ; Scott & Collinson : 130, PI. 1, figs. 6-10 

PI. 2, fig. 30. 

1961 Polygnathus communis Branson & Mehl ; Freyer : 70. 

1962 Polygnathus pura Voges; Miiller : 1388, text-fig. 2a, b. 

1964 Polygnathus communis communis Branson & Mehl ; Rexroad & Scott : 33, PI. 2, 

figs. 17, 18. 
1964 Polygnathus communis Branson & Mehl ; Higgins, Wagner-Gentis & Wagner : 225, 

PI. 5, fig. 30. 

1964 Polygnathus communis Branson & Mehl ; Budurov & Tschurner : PI. V, figs, ia, b, 
2a, b, 12, 18. 

1965 Polygnathus communis Branson & Mehl ; Spasov : 95, PI. 2, figs. 15, 15a. 
1965? Polygnathus communis Ethington : 581, PI. 67, fig. 7. 

Material. 740 specimens : figured, X 346, X 347, X 348. 
Range. North Crop KL 3-ZL 10, Avon Gorge K 3-C 9. 

Description. The platform varies in shape from ovate to lanceolate, but is 
unornamented except for a medial nodose carina. The platform edges tend to be 
upturned and thickened. The anterior blade varies in length but is commonly equal 
to the platform length, bearing from 10 to 16 laterally compressed, fused denticles ; 
the oral outline of the blade is convex. 

In aboral view the cavity is fairly large, circular, and situated at the junction of the 
platform and the anterior blade. In some specimens the cavity appears on the blade. 
The aboral surface of the unit posterior to the cavity tends to be concave. The 
cavity is extended as a tapering slit along the anterior blade, to a point just anterior 
to its mid point. A keel runs from the margin of the main cavity to the posterior tip 
of the platform ; its aboral surface may bear a fine groove. The aboral surface 
makes a sharp obtuse angle with the lateral faces of the outer platform margins, 
giving a chine-like aboral appearance to the unit. 

Remarks. Carinate and bifurcate subspecies of Polygnathus communis known 
from America are not present in our fauna, but the species is very variable throughout 
the section. A single specimen (PI. 12, ia-c) is obviously close to individual speci- 
mens assigned to this species, but differs in the general form of the oral surface of the 
platform. The anterior lateral margins of the platform are strongly constricted and 
upturned, giving almost a Siphonodella-like appearance to the anterior portion. The 
posterior portion is wide, shallow and bluntly rounded posteriorly, the whole having 
the general appearance of a shallow spoon. There is no ornamentation and the 
carina continues as a series of distinct blunted nodes to the posterior end of the 



184 



BRITISH AVONIAN CONODONT FAUNAS 



platform, the most posterior node being the smallest of the six exposed on the 
broken specimen. 

Polygnathus bischoffi sp. nov. 
Plate 13, figs. 8a-nc 

1957 Polygnathus inornata E. R. Branson ; Bischoff : 42, PI. 2, figs. 17, 18, 20, 21. 
1959 Polygnathus cf. flabella Branson & Mehl ; Voges (partim) : PI. 34, fig. 11 only. 
1964 Polygnathus inornata E. R. Branson ; Higgins : 225, fig. 4, PI. V, fig. 29. 

Derivation of name. After Dr. G. Bischoff. 

Diagnosis. Arrow-shaped platform ; widest in anterior half, tapering to pointed 
posterior. Unit usually slightly arched in lateral view. Platform ornamented by 
delicate ribs, confined to margin. Platform margin upturned in anterior half. Small 
basal cavity, circular in outline, with thickened lips, situated anteriorly. 

Material. 64 specimens : Holotype X 349, Paratypes X 350, X 351, Hypotype 
X 352 (all figured). 

Type locality and horizon. South Wales Coalfield. Sample SCC, C Zone, Fall 
Bay, Gower. 

Range. Avon Gorge C 11-C 24. 

Description. The platform is arrow-shaped, with a straight to slightly curved 
axis. In lateral view the unit is arched. The platform is widest anteriorly, and at 



Anterior blade 
ANTERIOR 



Oral surface 




Platform 



POSTERIOR 



LATERAL VIEW 




Carina 



Platform 



Cavity 



Cnine 



ORAL VIEW 



ABORAL VIEW 



Fig. 37. Polygnathus sp. showing morphological terms used in the text. 



BRITISH AVONIAN CONODONT FAUNAS 185 

mid-length it is only slightly narrower than at the anterior. The platform is two and 
a half times as long as wide and tapers to the pointed posterior. The margins of the 
platform are slightly upturned in the anterior and mid-thirds, and the oral surface is 
ornamented by a number of transverse ridges, which are more strongly developed at 
the margin. The margins of the platform are equal in height to the carina and on 
either side of the carina there is a trough, which is more strongly developed at the 
anterior. The trough opens to the anterior. The anterior blade is of the same length 
as the platform and consists of 6 denticles, which are highest at mid-length. The 
carina consists of nodes fused for their entire length and extends a short distance 
beyond the posterior extremity of the platform. The basal cavity; situated in the 
anterior third of the aboral surface, is small and rounded in outline, with thick lips. 
In some specimens a groove extends posteriorly from the basal cavity to the posterior 
extremity of the unit. 

Remarks. Compared with Polygnathus inornatus inornatus the platform of P. 
bischoffi is more elongate, broader in the anterior half and tapering uniformly in the 
posterior half. The platform also has more convex margins and is arched in lateral 
view. Polygnathus bischoffi has less strongly developed anterior troughs than 
Polygnathus inornatus inornatus, because the margins of the platform in the anterior 
third are not as strongly upturned. 

Polygnathus bischoffi is characteristic of the C Zone both in the Bristol area and in 
other parts of the South West Province. It makes its first appearance near the base 
of the Laminosa Dolomites. Bischoff obtained the specimens of Polygnathus 
inornatus which he illustrated from the Cu II Siphonodella Subzone. A specimen, 
which Voges referred to as Polygnathus cf. flabellus, and which is here placed in 
synonomy, was found by him in the Siphonodella p. triangulus triangulus Zone, 
which is Upper Cu I in age. 

The " Polygnathus inornata " group 

Rexroad & Scott (1964 : 35) remarked that " P. inornata is a remarkably varied 
species ". They included within their concept of this species P. Sagittarius Young- 
quist & Patterson, a junior synonym of P. lacinatus Huddle which we regard as a 
separate and variable species in its own right. However, even within the much 
narrower terms of our present diagnosis, there is still a marked degree of variability. 

The transition between P. inornatus and P. lobatus was noted by Rexroad & Scott 
(1964 : 35), and can also be seen in our faunas. There is also a tendency for the 
development of a rostral ridge in both P. inornatus and P. lobatus. In a few cases, 
breakdown of the transverse platform ridges into transverse lines of nodes is also 
seen. The P. inornatus fauna occurs within the range of the genus Siphonodella and 
these morphological details are characteristic of that genus, which is extremely rare 
(°'5% °f total conodont fauna) in our faunus. It seems that the P. inornatus group 
show morphological developments which carry it towards, but not as far as, the 
characteristic morphology of the genus Siphonodella. 

The P. inornatus s.s. forms with a well-developed rostral ridge are here given sub- 



iSo 



BRITISH AVONIAN CONODONT FAUNAS 



specific rank as P. inomatus rostratus and the P. lobatus forms with the same feature 
are referred to P. lobatus inflexus. 



Polygnathus inomatus inomatus Branson & Mehl 
Plate 10, figs. 4a-6c 



1934 

1934 

1938 

non 1939 

1944 
1949 

1949 
1951 

non 1956 

1956 

non 1957 

non 1957 

1957 
non 1958 

1959 

non 1964 

1964 



Polygnathus inornata Branson & Mehl : 
Polygnathus inornata Branson & Mehl ; 
Polygnathus inornata Branson & Mehl ; 
Polygnathus inornata Branson & Mehl ; 
gnathus inornata rostrata). 
Polygnathus inornata Branson & Mehl ; 
Polygnathus inornata Branson & Mehl 
figs. 4l 5, 9, 13. 

Polygnathus inornata Branson & Mehl ; 
Polygnathus inornata Branson & Mehl ; 



293, PI. 24, figs. 5-7. 
E. R. Branson : 309, PI. 25, figs. 8, 26. 
Branson & Mehl : 132, 146, PI. 34, fig. 37. 
Cooper : 400, PI. 39, figs. 11, 12 (—Poly- 

E. B. Branson : PI. 39, fig. 37. 

; Youngquist & Patterson : 64, PI. 17, 

Thomas : 409, 411, PI. 3, fig. 36. 
Youngquist & Downs : 787, 788, PI. 111, 



figs. 17, 18 (non PI. in, fig. n=P. lobata lobata). 



Polygnathus inornata Branson & Mehl ; 
(=P.flabella). 

Polygnathus inornata Branson & Mehl ; 
Polygnathus inornata Branson & Mehl 
(=P. lacinata lacinata). 
Polygnathus inornata Branson & Mehl 
fig. 7 (=P. nodomarginata) . 
Polygnathus inornata Branson & Mehl ; 
Polygnathus inornata Branson & Mehl ; 
Polygnathus inornata Branson & Mehl ; 
figs. 17-20 = P. lacinata lacinata). 
Polygnathus inornata Branson & Mehl ; 
PI. 5, fig. 29 (=P. lacinata lacinata). 
Polygnathus inornata Branson & Mehl ; 



Bischoff & Ziegler : 157, PI. 12, figs. 4, 5 



Hass : 25, PI. 2, figs. 14, 15. 
Bischoff : 42, PL 2, figs. 17, 



20, 21 



; Ziegler in Fliigel & Ziegler : 46, PI. 2, 

Cloud, Barnes & Hass : PI. 5, fig. 6. 
Klapper : 1089, PI. 142, figs. 2, 3. 
Voges : 291, PI. 34, figs. 12-16, (non PI. 34, 

Higgins, Wagner-Gentis & Wagner : 225, 

Rexroad & Scott 35, PI. 2, figs. 19, 20. 



Material. 82 specimens : figured, X 353, X 354, X 355. 
Range. North Crop KL 16-KL 20. 

Description. The platform is semi-circular in cross-section and is ornamented 
by transverse ribs, which terminate on the platform edge as low nodes. The ridges 
may break up into transverse rows of nodes. The platform is fairly flat at the 
posterior, but anteriorly it has deep troughs, separated by a nodose carina. The 
whole unit is nearly symmetrical. 

The carina is a continuation of the free blade, and runs the whole length of the 
platform, terminating at the posterior end in a point. The blade is thin and highest 
in its mid-part, the aboral outline being straight. 

Aborally the unit is keeled, the basal cavity occurring as a small pit at, or just 
posterior to, the junction of the anterior blade and the platform. The cavity edges 
tend to be thickened. 



Remarks. Our specimens agree closely with those of Rexroad & Scott (1964). 



BRITISH AVONIAN CONODONT FAUNAS 187 

Polygnathus inornatus rostratus subsp. nov. 

Plate 10, figs. ja.-gc 

? 1939 Polygnathus irregularis Cooper : 400, PI. 39, figs. 57, 58. 
1962 Pseudopolygnathus ? cf. Pseudopolygnathus triangula Voges ; Miiller : 1388, text-figs, 
ga-c. 

Derivation of name. From the development of a rostral ridge on the inner 
platform. 

Diagnosis. P. inornatus possessing rostral or pseudorostral ridge on inner 
platform. 

Material. 28 specimens : Holotype X 530, Paratypes X 356, X 357 (all 
figured). 

Type locality and horizon. North Crop. Sample KL 4. 

Range. North Crop KL 4-KL 16-KL 20, ZL i, Avon Gorge K 12-K 14. 

Description. Specimens of P. inornatus rostratus agree closely with specimens 
of P. inornatus s.s., apart from the configuration of the inner margin. There is a 
tendency for the anterior part of the inner margin to move towards the anterior 
blade, the posterior part then becoming lobate. The anterior inner margin tends to 
run towards the carina for a very short distance in more advanced forms. 

In some cases there tends to be a thickening of the aboral portion of the platform 
wall, so that in oral view the platform edge does not form the inner edge of the unit. 

Remarks. This subspecies includes all specimens showing a breakdown in the 
smoothness of the inner edge. Thus in more advanced forms a pseudo-rostral ridge 
can be seen (e.g. PI. 10, fig. 7b). In less advanced forms there may be thickening of 
the aboral edge and a breakdown of the curvature of the inner edge (e.g. PI. 10, 
fig. 9b). The strength of development of the ridge bears some relationship to both 
ontogeny and to stratigraphic position. This involves an offset, tilt and deflection 
towards the carina of the inner lateral margin, the pseudo-rostral ridge having a 
sharp and well-defined outer face. The posterior portion of the ridge, which runs 
sub-parallel to the carina, is conspicuously higher than the adjacent inner margin, 
although the posterior termination is low and indistinct. 

Polygnathus inornatus vexatus subsp. nov. 
Plate 10, figs. ia-3c 

Derivation of name. From the troublesome problem of specific assignment. 

Diagnosis. Subspecies of P. inornatus. An arched unit with symmetrical 
platform, curved axis, and fairly long blade, composed of broad, fused, chevron- 
tipped denticles. Carina low, nodose, extending beyond platform as short posterior 
blade. Symmetrical lanceolate platform, ornamented with medium to strong 
transverse ribs ; platform edges serrated. Basal cavity small, occurring near 
junction of blade and platform. 

Material. 5 specimens : Holotype X 358, Paratypes X 359, X551 (all figured) . 



[88 BRITISH AVONIAN CONODONT FAUNAS 

Type locality and horizon. North Crop. Sample KL 19. 

Range. North Crop KL 17-KL 19, Avon Gorge K 17. 

Remarks. As was noted by Rexroad & Scott (1964) P. longiposticus belongs to 
the P. inornatus group of polygnathids. It can be distinguished from P. inornatus 
s.s., by the lanceolate platform and the longer free blade. The present subspecies 
approaches P. longiposticus in these respects. 

Polygnathus lacinatus Huddle 

Certain polygnathids with a lanceolate platform and an elongate, excavated cavity 
were referred to a new species, P. lacinatus, by Huddle (1934). This species was 
recognized by Cooper (1939), but Youngquist with various co-authors (Youngquist & 
Patterson 1949, Youngquist, Miller & Downs 1950, and Youngquist & Downs 1951), 
referred similar forms to P. Sagittarius Youngquist & Patterson. German workers, 
describing collections from condensed sequences of strata, included P. lacinatus 
within the species P. inornatus E. R. Branson, thus extending both the stratigraphic 
range and concept of that species. The distinctive feature of P. lacinatus is the 
marked longitudinal extension of the rim of the basal cavity, which is often half the 
total platform length (e.g. PI. 11, fig. 9b). 

P. lacinatus appears to us to be a valid species. It is restricted to an interval 
comparable with beds of Cu II fi/y age in Europe. Its generic affinities are somewhat 
doubtful. Huddle stated that the platform was a perfect polygnathid platform, 
although the basal cavity differs markedly from the " typical " cavity of that genus. 
The possession of a large basal cavity brings it within the morphological scope of the 
genus Pseudopolygnathus, but the lack of asymmetry of the cavity and the poly- 
gnathid nature of the platform lead us to conclude, like Huddle, that this form is a 
polygnathid. Later phylogenetic work may show that this is not the case. Within 
our faunas there appear to be several variants, and these have been referred to new 
subspecies. Forms referred to P. lacinatus lobatus show lobation of the posterior 
part of the outer platform, and considerable narrowing of the anterior part of the 
platform, with upturning of the platform edges. This tends to give these specimens 
an overall siphonodellid appearance, but the basal cavity and lack of rostral ridges 
set them apart from the genus Siphonodella. 

Polygnathus lacinatus asymmetricus subsp. nov. 
Plate 11, figs. ia-4c 

Derivation of name. From the asymmetrical development of the platform. 

Diagnosis. Subspecies of P. lacinatus with reduced inner platform, giving 
asymmetrical platform outline. 

Material. 295 specimens : Holotype X 361, Paratypes X 360, X 362, X 363 
(all figured). 

Type locality and horizon. North Crop. Sample ZLA 32. 



BRITISH AVONIAN CONODONT FAUNAS 189 

Range. North Crop ZLA 29-ZLA 33. Avon Gorge Z 33-C 20. 

Description. The anterior blade and the anterior portion of the platform are 
exactly comparable with P. lacinatus s.s., but the posterior part of the inner platform 
is reduced and does not extend to the posterior termination, the carina being 
extended posteriorly as a short posterior free blade. 

Polygnathus lacinatus circaperipherus subsp. nov. 
Plate ii, figs. I2a-i5c 

Derivation of name. From the platform edge, which encircles the posterior 
portion of the platform. 

Diagnosis. P. lacinatus with platform margin complete around posterior part of 
platform ; posterior section of carina obsolescent. 

Material. 32 specimens : Holotype X 364, Paratypes X 365, X 366, X 367 
(all figured). 

Type locality and horizon. North Crop. Sample ZLA 32. 

Range. North Crop ZLA 17-ZLA 30, Avon Gorge C 7. 

Description. This subspecies is very similar to P. lacinatus except for the 
posterior platform termination. The platform edge is wrapped around the posterior, 
the carina dying away before it reaches the posterior. In aboral view the keel is also 
terminated abruptly and the whole posterior of the unit is rounded off. The 
posterior outline may be expanded and club-like (e.g. PI. 11, fig. 12b) to bluntly 
pointed (e.g. PI. 11, fig. 15a). There is some variation in the form of the basal 
cavity. In some specimens it is extended relatively further posteriorly than in 
others. In neither case, however, is there an ungrooved posterior keel developed 
behind it. 

Remarks. This morphological variation is also seen in our faunas in the species 
of P. communis. 

Polygnathus lacinatus lacinatus Huddle 
Plate 11, figs. 8a-ioc 

1934 Polygnathus lacinata Huddle : 95, PI. 8, figs. 1-3. 

J 939 Polygnathus lacinata Huddle ; Cooper : 401, PI. 40, figs. 3, 4. 

1949 Polygnathus sagittaria Youngquist & Patterson : 66, PI. 15, figs. 9, 10. 

1950 Polygnathus aff. Polygnathus sagittaria Youngquist & Patterson ; Youngquist, Miller & 
Downs : 527, PI. 67, figs. 2-4. 

1951 Polygnathus sagittaria Youngquist & Patterson ; Youngquist & Downs : 788, PI. 111, 
figs. 7-9- 

1959 Polygnathus inornata E. R. Branson ; Voges : 291, PI. 34, figs. 17-20 (non PI. 34, 
figs. 12-16 = P. inornata). 

Material. 753 specimens : figured, X 368, X 369, X 370. 
Range. North Crop ZLA 29-ZL 19, Avon Gorge Z 32-C 20. 



igo BRITISH AVONIAN CONODONT FAUNAS 

Description. The platform is lanceolate, from two to three times as long as wide, 
being widest at mid-point, narrowing considerably both to the anterior and to the 
posterior. The platform ornament consists of a fairly strong carina, often extended 
beyond the platform as a short posterior blade, the nodes being slightly higher in this 
region. There is an unornamented trough on either side of the carina, accentuated by 
the upturning of the platform edges, especially in the anterior. The upturned 
platform edges bear short transverse ridges, terminating in denticles, which give a 
crenulate platform edge. The ornament varies considerably ; the juveniles tend 
to be smooth, and the strength of the ridges varies in the adults. The anterior 
blade is fairly long and high, consisting of 7 to 8 tall, laterally compressed, fused 
denticles, which are highest at the anterior end and decrease regularly in height 
towards the junction with the platform. 

In aboral view the unit is very distinctive, the basal cavity being large and 
elongate. It tends to close slightly with age, but is always extremely large, being 
widest at the anterior, and narrowing gradually towards the posterior, where a short 
grooved keel is present. 

Remarks. This subspecies is distinguished by the large basal cavity. Forms 
described as P. marginatus Branson & Mehl, by Rexroad & Scott (1964 : 37) are 
recorded as having large basal cavities and may be referable to P. lacinatus s.s., but 
the lack of an aboral illustration makes us hesitate to include them in the present 
synonomy. Orally this subspecies is highly variable, and some forms might be 
mistaken for P. inornatus. The most distinctive feature is, however, the form of the 
basal cavity. In this, apart from the length of the basal cavity proper, the most 
conspicuous feature is the very strong lateral and longitudinal extension of the lips 
around the cavity. These extend posteriorly to the cavity, and become obsolescent 
only in the posterior quarter of the unit, although they narrow posteriorly towards 
that point from their maximum at the posterior termination of the cavity. There is 
no chine-like structure on the aboral surface, and the low-angle sloping outer aboral 
margins of the platform join the lateral lips of the cavity at a sharp angle. Most 
specimens tend to show an almost siphonodellid development of the anterior end of 
the platform, though this itself shows some variation. The Siphonodella-like spout 
of P. lacinatus prelobatus is even more strongly developed than that of the present 
subspecies. The strongly developed posterior aboral extension of the carina, and 
the deep anterior blade give a distinctive appearance to the platform in lateral view. 
It tends to " ride high " on the surface of the lateral blade. 



Polygnathus lacinatus prelobatus subsp. nov. 
Plate 11, figs. 5a-7b, na-c 

Derivation of name. From the lobate nature of the inner platform. 

Diagnosis. Subspecies of P. lacinatus with lobate postero-inner platform. 

Material. 179 specimens : Holotype X 371, Paratypes X 372, X 373, X 374 
(all figured). 



BRITISH AVONIAN CONODONT FAUNAS 191 

Type locality and horizon. North Crop. Sample ZLA 32. 

Range. North Crop ZLA 29-ZLA 33, Avon Gorge Z 33-C 9. 

Description. The free blade and outer platform are closely similar to P. lacinatus 
s.s., but there is modification of the inner posterior platform margin. The postero- 
inner portion tends to be produced as a lobe, narrowing rapidly to the posterior 
termination, which is formed by a posterior projection of the carina, to give a short 
posterior anterior blade. The anterior inner platform tends to be considerably 
upturned and the platform edge is very close to the anterior blade. In aboral view 
the unit exhibits the characteristics of P. lacinatus s.s. 

Remarks. The narrowing of the anterior portion of the platform and the lobation 
of the posterior inner platform give this subspecies the aspect of Siphonodella, but the 
basal cavity precludes the inclusion of these forms in this genus. 



Polygnathus lobatus lobatus Branson & Mehl 
Plate 9, figs. 5a-8c 

1938 Polygnathus lobata Branson & Mehl : 146, PI. 34, figs. 44-47. 

1939 Polygnathus lobata Branson & Mehl ; Cooper : 401, PI. 39, figs. 29, 30. 
J 939 Polygnathus curta Cooper (partim) : 400, PI. 39, figs. 37, 38 only. 
1949 Polygnathus lobata Branson & Mehl ; Thomas : 411, 418, PI. 3, fig. 11. 
1949 Polygnathus cunulae Youngquist & Patterson : 62, PI. 15, figs. 11-15. 

195 1 Polygnathus inornata Branson & Mehl ; Youngquist & Downs : 787, PI. in, fig. 11 

(non PI. in, figs. 17, 18 = P. inornata inornata). 
1957 Polygnathus lobata Branson & Mehl ; Bischoff : 42, PI. 2, fig. 19. 
1964 Polygnathus lobata Branson & Mehl ; Rexroad & Scott : 35, PI. 2, figs. 15, 16. 

Material. 21 specimens : figured, X 376, X 377, X 378, X 440. 
Range. North Crop KL 16-KL 20. 

Description. This unit is boat-shaped, with a curved axis. The platform is flat 
in the posterior portion but deepens to form two troughs either side of the carina in 
the anterior portion. The unit tends to be symmetrical in the anterior half, but in 
the posterior, the outer platform wall flares out to give a lobate process. The plat- 
form then narrows rapidly to give a pointed posterior termination. The ornament 
consists of transverse ridges dying out towards the carina and terminating on the 
platform edges as low nodes or short chevron-shaped denticles. The carina is 
sinuous, consisting of low nodes which merge with the free blade, which is itself short 
and high, being highest at its mid point. 

In aboral view the unit is keeled, there being a small cavity posterior to the junc- 
tion of the free blade with the platform. The antero-lateral corners project as two 
" horns " in aboral view. The whole central part of the aboral surface tends to be 
more or less flat and unornamented, except for the sinuous median ridge. The outer 
margin of this flattened chine-like area is sharp, and the flat sloping faces of the outer 
aboral edges join it at a sharp angle. The surface of the chine is finely striate, with 
the striations more or less parallel to the outer margins. In at least some specimens 



(92 BRITISH AVONIAN CONODONT FAUNAS 

(e.g. PI. 9, fig. 6a-c, X 376), the aboral cavity is situated about a quarter of the total 
length of the platform from the anterior end. 

Remarks. This form is distinguished from P. inomatus s.s. by possessing a lobe 
on the outer margin. The two subspecies appear to be transitional. 

Polygnathus lobatus inflexus subsp. now 
Plate 9, figs. 9a-c 

Derivation of name. From the inflexing of the inner platform margin. 

Diagnosis. P. lobatus in which inner anterior lateral margin is more or less 
strongly inflexed. 

Material. 4 specimens : Holotype X 375 (figured). 

Type locality and horizon. North Crop. Sample KLM 1. 

Range. North Crop KL 16-KL 20, Avon Gorge K 12. 

Description. In a few specimens whose general characteristics are similar to P. 
lobatus lobatus, there is a marked tendency for the inflexing and upraising of the inner 
anterior lateral margin of the platform. This tends to be confined to the anterior 
third or half of the platform. The oral edge bears a series of irregular, low, rounded, 
confluent denticles, giving a bluntly serrate margin. It stands conspicuously higher 
than the carina and rather higher than the opposing outer lateral margin. It reaches 
almost the height of the large denticles in the median portion of the anterior blade, 
and it runs broadly sub-parallel to the line of the anterior portion of the carina. It is 
at the posterior end of this inflexed portion that the carina tends to be more or less 
strongly laterally deflected. 

Remarks. This form appears to be undergoing similar adaptations to those of 
P. inomatus rostratus within the species P. inomatus. This may imply either close 
relationships between P. lobatus and P. inomatus or independent (functional?) 
convergence. 

Polygnathus sp. 
Plate 15, figs. 9a-c 

Material, i specimen : figured, X 531. 

Range. Farlow Sample FAR 4A. 

Description. This specimen seems to be a pathological individual of the genus 
Polygnathus. It is distinguished by a lip-like secondary development on the inner 
lateral platform, so that although the anterior edge of the platform forms a typical, 
open, spout-like development on the inner lateral side and the inner anterior lateral 
margin, it is strongly developed and upturned. It ceases after running for about a 
quarter of the total length of the platform, and the platform itself is then bent 
outwards, as though some injury had taken place to the individual and then been 
reformed. The rather low sinuous margin of the platform gives a wide platform for 



BRITISH AVONIAN CONODONT FAUNAS 193 

the middle half, but the whole platform is sharply tapered and is pointed posteriorly. 
There is a conspicuous lack of general ornament, except for barely perceptible 
transverse ridges and nodes on the outer lateral faces, and a median carina, which is 
also very inconspicuous, consisting of low fused nodes, which runs posteriorly from 
the anterior blade but does not divide the platform into two equal halves. It runs 
into the posterior portion of the platform. The anterior inner edge is higher than 
any other part of the platform except the median outer lateral edge, and is 
ornamented by low fused nodes, up to six in number. 

In inner lateral view the " injury " to the inner lateral platform makes a prominent 
feature. The platform is deepest anteriorly and the " injury " shows a secondary 
projection. 

In aboral view the individual shows a typical polygnathid form, with a minute and 
thickly-lipped cavity restricted to the anterior fifth of the platform, and extended 
anteriorly and posteriorly as a slit-like groove. The anterior blade is poorly 
preserved but it is relatively short, with a rounded anterior aboral margin, and has at 
least one conspicuous denticle near its posterior end. 

Polygnathus sp. 

Plate 31, fig. 21 

Material. 3 specimens : figured, X 130. 

Range. Avon Gorge D 22. 

Description. Rexroad (1957 : 41) has noted the presence of small numbers of 
polygnathids in the Renault Formation at two localities. He has described three 
fragments, and very small numbers of specimens are also present in the D Zone of the 
Avon Gorge and the North Crop. In all three cases this represents an abnormally 
high stratigraphic occurrence of the genus. In the Mississippi Valley, for example, 
its generally accepted range extends upwards only into the Burlington Formation. 
A single specimen is illustrated. The anterior blade is broken, but this specimen 
displays strongly developed aboral lips with a conspicuous pit developed near the 
anterior end of the platform, and a well-developed slit-like basal cavity extending the 
whole length of the platform. 

Genus PRIONIODINA Ulrich & Bassler 1926 

1925 Prioniodina Bassler : 219 (nom. nud.). 

1926 Prioniodina Ulrich & Bassler : 17, 18. 
1934 Subbryantodus Branson & Mehl : 285. 

Type species. Prioniodina subcurvata Ulrich & Bassler 1926. 

In 1925 Bassler erected the generic name Prioniodina, and in 1926 with Ulrich as 
senior author, he gave the following description : " Base of tooth more or less 
curved, crowned with numerous, sub-parallel, rounded, discrete denticles all inclined 
in one direction, one of which located in the median third, is considerably larger than 
the others. " 



194 



BRITISH AVONIAN CONODONT FAUNAS 



Later, Branson & Mehl (1934A) erected the genus Subbryantodus for " arched 
denticulate bars . . . with one or both limbs laterally flexed . . . denticles . . . 
laterally compressed . . . closely crowded . . . one denticle of exceptional size, 
the apical denticle at the apex of the arch . . . the aboral edge of the bar excavated 
beneath the arch apex by a long pit that tends to extend as a distinct groove along 
the edge of each limb ". 

Branson & Mehl suggested (p. 285) that Stibbryantodus differed essentially from 
Prioniodina in the fused, laterally compressed denticles and tendency toward a split 
aboral edge. We consider that these differences are not of generic significance and 
regard Subbryantodus as a junior subjective synonym of Prioniodina Bassler 1925. 



Prioniodina eireica (Collinson & Druce) 

Plate 28, fig. 13 

Subbryantodus eireica Collinson & Druce (in press). 

Material, i specimen : figured, X 315. 

Range. North Crop 3D 17. 

Description. The distinctive features of this species are the minutely denticu- 
lated and very short depressed anterior bar, the massive, recurved, wide, pointed 
apical denticle, and the short straight feebly denticulated posterior bar. Below the 



Apical denticle 

Blade denticles 



Posterior_ 
bar 




Anterior bar 



Basal cavity 



Fig. 38. Prioniodina sp. showing morphological terms used in the text. 



BRITISH AVONIAN CONODONT FAUNAS 195 

posterior edge of the apical denticle there is a strongly flared basal cavity which, 
although laterally wide, is not very deep. 

The whole unit is rather small and short and the apical denticle looks altogether 
too large for the general proportions of the anterior and posterior bars. The 
anterior bar is short, strongly recurved and slender in general construction, making 
an angle of about 130 ° with the straight basal margin of the posterior bar in outer 
lateral view. The anterior bar bears 2 or 3 small denticles with blunt free tips, but 
otherwise basally confluent. They have a tendency to increase in size posteriorly 
and stand more or less erect, or only gently posteriorly inclined, to the anterior bar. 
The anterior bar is of more or less uniform depth throughout its length, though it 
may be a little shallower anteriorly. 

The apical denticle is strongly recurved on its anterior edge, but its posterior edge 
is straight or only feebly curved. It is sharply pointed and very broad at its base, 
being about five or six times as wide as the largest adjacent denticles. It has sharp 
anterior and posterior edges and gently convex lateral faces. The posterior bar is 
short and minutely denticulate, the denticles being so closely crowded that they are 
virtually confluent, except for their blunted tips. The bar decreases in depth 
posteriorly and is slightly longer, though shallower than, the anterior bar. 

The other conspicuous feature of the unit in outer lateral view is the widely flaring 
basal cavity, which forms a conspicuous feature below the posterior half of the apical 
denticle. It is less conspicuous in inner lateral view and the whole unit is slightly 
bowed inward, having flatter faces. 

In aboral view the basal cavity is seen to be asymmetrical, being more widely 
flared on the outer lateral face than it is on the inner. On the inner lateral face, 
although there is less curvature, the convexity continues towards the tip of the 
posterior bar. The whole posterior bar, as well as the posterior half of the apical 
denticle, is excavated by the cavity, which is deepest below the posterior edge of the 
apical denticle. It is continued anteriorly as a minute slit. 

Remarks. Collinson and Druce have discussed the relationship of this species to 
similar species of the genus Ozarkodina. 

Prioniodina laevipostica (Rexroad & Collinson) 

Plate 28, figs. n-i2b 

1963 Ozarkodina laevipostica Rexroad & Collinson : 19, PI. 1, figs. 1-6. 

Material. 31 specimens : figured, X 316, X 317. 

Range. North Crop ZLA 6-ZLA 12, CYD 6-CYD 7. 

Description. This species closely approaches P. eireica, but differs from it in the 
relatively stronger development of the anterior and posterior bars, the less massive 
apical denticle, and the rather less conspicuous basal cavity. Rexroad & Collinson 
(1963) noted that their species had a posterior bar which was only partly denticulate, 
but both their illustrations and the present specimens show that, in at least some 
individuals, the posterior bar is denticulate for most or all of its length. The present 



ig6 BRITISH AVONIAN CONODONT FAUNAS 

individuals bear up to five closely set, but apically discrete, more or less sharply 
pointed denticles, which decrease in size posteriorly and which are inclined at about 
45 to the aboral surface of the posterior bar. The posterior bar is deep in its 
anterior portion but tapers rapidly towards its posterior end. Its aboral margin is 
more or less straight. 

The apical denticle is two to three times the width of the largest adjacent denticles 
and is sharply to bluntly pointed. There is considerable variation in the form of the 
distal end of the apical denticle (see Rexroad & Collinson 1963). Although the 
cavity is similar in general form, it is rather shallower and somewhat less asymmetrical 
than that of P. eireica, and its anterior extension is also rather more conspicuous. 
The edges of both the cavity and the slits along the anterior and posterior bars are 
also prominent. 

Remarks. Our specimens from the D Zone closely resemble those of Rexroad & 
Collinson in overall morphology and in the aboral configuration, but they differ in 
denticulation, our specimens having fewer denticles on the anterior bar and more on 
the posterior bar. However, Rexroad & Collinson mention that some of their 
specimens fall within the limits of our specimens. The variable dentition is thus 
due to variation within the species. 



Prioniodina latericrescens (Branson & Mehl) 
Plate 24, fig. 19 
1934 Lonchodina latericrescens Branson & Mehl : 212, PI. 14, fig. 20. 

Material. 12 specimens : figured, X 429. 

Range. North Crop KL i-ZLA 4. 

Description. The unit is bowed and arched, being laterally compressed in 
juveniles, but the bars becoming circular in cross-section in adults. The posterior 
and anterior bars are of equal length, bearing about 4 isolated, sub-circular, 
posteriorly inclined denticles. In aboral view the pit is fairly large and occurs 
beneath the apical denticle. 



Prioniodina oweni sp. nov. 
Plate 28, figs. 5a-c 

Derivation of name. After Mr. T. R. Owen. 

Diagnosis. Prioniodinid with greatly expanded basal cavity and restricted 
posterior bar. 

Material. 13 specimens : Holotype X 330 (figured). 

Type locality and horizon. R. Clydach, Nr. Gilwern, Lower Z Zone. Sample 
ZLA5. 



BRITISH AVONIAN CONODONT FAUNAS 197 

Range. North Crop ZLA 3-ZLA 27. 

Description. The anterior bar is short, bearing about 5 discrete, sub-circular, 
posteriorly inclined denticles, whose height increases posteriorly, culminating in the 
apical denticle, which is the largest. The posterior bar is very restricted, commonly 
bearing 1 or 2 small, discrete, sub-circular, posteriorly inclined denticles. 

In aboral view the whole unit is excavated, the basal cavity being expanded and 
pear-shaped at the posterior end. The widest part occurs beneath the apical denticle 
and it narrows gradually beneath the anterior bar, and rapidly beneath the posterior 
bar. The posterior termination tends to be rather blunt. The cavity lips in the 
posterior part are thickened to give a small flange. 

Remarks. The large basal cavity with excavated bars, together with the short 
posterior bar, precludes the placing of this species within the genus Ozarkodina, and 
serve to distinguish it from all other prioniodinids. 

Prioniodina prelaevipostica sp. nov. 
Plate 24, figs. 1-6 

Derivation of name. Ancestral form of Prioniodina laevipostica (Rexroad & 
Collinson) . 

Diagnosis. Short Prioniodina, with large apical denticle and deflected anterior 
bar. 

Material. 9 specimens : Holotype X 334, Paratypes X 333, X 331, X 332, 
X 335. X 336 (all figured). 

Type locality and horizon. R. Clydach, Nr. Gilwern, uppermost Z Zone. 
Sample ZLA 33. 

Range. North Crop ZLA 32-ZL 19. 

Description. The whole unit is arched, being surmounted by a tall, laterally 
compressed, free standing, posteriorly inclined apical denticle. The anterior bar is 
short, depressed through 45 ° and slightly deflected, bearing 2 or 3 tall isolated 
denticles, the most anterior ones being very small and posteriorly inclined. 

The posterior bar is longer than the anterior, being fairly deep, shallowing 
posteriorly, and bearing 4 or 5 triangular denticles which are laterally compressed 
and posteriorly inclined. 

In aboral view the unit is excavated beneath the apical denticle and the posterior 
bar, the cavity having flared lips. Beneath the anterior bar there is a narrowing 
groove. 

Remarks. This species is very similar to P. laevipostica (Rexroad & Collinson) 
which should be referred to the genus Prioniodina. The two species differ in the 
degree of curvature of the anterior bar, our species being much less curved, and in the 
dentition of the posterior bar, on which P. laevipostica bears 4 or 5 well-formed 
denticles. The obvious morphological similarities of these two species lead us to 
believe that P. prelaevipostica is the precursor of P. laevipostica. 



i 9 8 BRITISH AVONIAN CONODONT FAUNAS 

Prioniodina stipans (Rexroad) 
Plate 28, figs. 7a-ioc 

1957 Subbryantodus stipans Rexroad : 39, PI. 4, fig. 1. 

1961 Subbryantodus stipans Rexroad ; Higgins : 219, text-fig. 6, PI. 12, fig. 14. 

1962 Subbryantodus stipans Rexroad ; Higgins : 13, text-fig. 2, PI. 1, fig. 9. 

Material. 105 specimens : figured, X 337-X 340. 
Range. North Crop 3D 10-3D 22. 

Description. The most distinctive features of this species are the relatively 
short but strongly curved general form, with a series of subequal pointed denticles, 
the apical denticle being only slightly larger than those of its neighbours, and the 
wide flaring and greatly longitudinally extended basal cavity. 

The basal cavity is greatly elongated and extends almost to the posterior end of the 
posterior bar, and about two-thirds the way to the end of the anterior bar. It is 
biconvex in outline, very deep, and slightly asymmetrical, with thin lateral edges. 
The anterior bar is about equal in length to the posterior, but is rather deeper, 
although it decreases slightly in depth anteriorly. The whole basal margin of the 
unit is deeply concave in inner lateral view and the anterior bar is conspicuously 
bowed inward. There is a rather inconspicuous shoulder developed about two-thirds 
of the height from the aboral margin to the base of the denticles. The anterior bar 
bears a series of about 12 denticles, confluent for most of their length, but bluntly 
pointed in their free apices. They have strongly convex lateral faces in their free 
portions and flat to gently convex lateral faces in their confluent portions, their free 
edges being more or less sharp. Those in the posterior two-thirds of the bar are of 
more or less uniform height and are regularly inclined posteriorly at about 45 ° to the 
bar, but those in the anterior third of the bar decrease in height towards the anterior 
end, and the most anterior two or three denticles are relatively inconspicuous and 
wholly confluent. 

The apical denticle is about twice as wide as the adjacent denticles, and is about 
twice as long as adjacent denticles of the anterior and posterior bars. It is inclined 
at about 45 ° to the adjacent aboral surface. 

The posterior bar is sharply recurved and bears a series of about 7 sharply pointed 
and partly fused denticles, which are strongly laterally compressed, and which tend 
to decrease in size posteriorly, especially in the posterior third. 



Prioniodina subaequalis (Higgins) 
Plate 28, figs, ia-4 

1961 Subbryantodus subaequalis Higgins : 218-219, PI- I2 > fig- *5> text-fig. 6. 
1963 Subbryantodus subaequalis Higgins ; Bouckaert & Higgins : 17, fig. 3. 
Subbryantodus subaequalis Higgins ; Collinson & Druce (in press). 

Material. 143 specimens : figured, X 341-X 344. 
Range. North Crop 3D 10-3D 22. 



BRITISH AVONIAN CONODONT FAUNAS 199 

Description. The most striking features of this species are the confluent denticles 
of the long anterior bar, and the large denticles of the posterior bar. There is no 
conspicuous apical denticle, and the denticles of the posterior bar are discrete. 

In aboral view the unit is straight in its median two-thirds, but both the anterior 
and the posterior ends are sharply flexed inwards. There is a deep and relatively 
conspicuous basal cavity below the apical denticle, and this is extended as a wide 
deep groove along the greater length of the anterior bar, and as a shorter narrowing 
groove below about half the length of the posterior bar. The edges of the cavity and 
of the aboral surfaces of the bars are relatively thin. 

This is a somewhat variable species, but the anterior bar is generally rather longer 
and deeper than the posterior, and tends to be rather straight along its aboral margin 
when seen in inner lateral view. It bears a series of 9 or 10 laterally compressed 
denticles which are confluent at their bases and which are inclined posteriorly. In 
some specimens they show an alteration in size, and they also show a general tendency 
to increase in size posteriorly. Their free edges are sharp and their lateral faces are 
strongly convex, especially in the posterior half of the anterior bar. They show 
some variation, in that in some specimens they are free for the greater part of their 
length, but this is a relatively unusual feature. 

There is no apical denticle in the strict sense, but the 2 or 3 denticles at the point 
of flexure of the unit tend to be larger than any of the other, and to be more or less 
equal in size. They are free for most of their length and they are inclined posteriorly, 
the degree of inclination increasing towards the posterior end of the series. They 
have sharp anterior and posterior edges and all taper sharply to their pointed tips. 
They have gently convex lateral faces. Behind them is a series of up to 5 discrete 
and strongly posteriorly inclined denticles, which in some specimens have smaller 
denticles separating them. There is a rather indistinct apical lip at the point of 
flexure. The posterior bar tends to decrease in depth posteriorly and its posterior 
aboral margin is gently curved. 

Prioniodina ? sp. nov. 
Plate 28, figs. 6a-c 

Material, i specimen : figured, X 345. 

Range. Scotland GILM 3. 

Description. A single specimen is tentatively referred to the genus Prioniodina. 
It is characterized by an elongate straight anterior bar, which is continuous, without 
any vertical flexure with the straight, but broken, posterior bar. The anterior bar 
has convex lateral shoulders on the inner lateral face, and a straight inner lateral face 
below them. Its oral surface bears 5 discrete short denticles with sharply pointed 
tips, and posterior edges which are sharp ; they taper uniformly from their point of 
origin and stand more or less erect or only slightly inclined to the anterior bar. 
They show a slight tendency to increase in height posteriorly. The posterior bar 
bears at least 3 closely spaced, but discrete, sharply-pointed denticles. That 
nearest to the apical denticle is larger than the other two. They are strongly 



2oo BRITISH AVONIAN CONODONT FAUNAS 

laterally compressed, with sharp anterior and posterior edges and gently convex 
lateral faces. The apical denticle is about three times as wide as the adjacent 
denticles and two to three times as long. Its sharp anterior and posterior edges 
taper uniformly to a point and it is gently inclined to the posterior bar. Along the 
whole inner lateral length of the anterior and posterior bars there is a more or less 
conspicuously convex shoulder below the point of origin of the denticles. In outer 
lateral view the whole unit is somewhat natter and the denticles are seen to curve 
slightly inwards. In aboral view the unit is excavated by a thin slit, which is very 
narrow anteriorly, but which increases regularly in width posteriorly, being widest 
posterior to the apical denticle, though there is no sign of lateral flare on the edges 
below the apical denticle. 

Genus PSEUDOPOLYGNATHUS Branson & Mehl 1934 

1934 Pseudopolygnathus Branson & Mehl : 297. 
1939 Macropolygnathus Cooper : 392. 

Type species. Pseudopolygnathus prima Branson & Mehl 1934. 

The origin and nature of the genus 

Pseudopolygnathus developed from Spathognathodus in the late Devonian and early 
Mississippian. Spathognathodus anteposicornis , S. plumulus plumulus sp. nov. and 
S. aculeatus have lateral denticles developed on one side of the blade and 5. costatus 
sulciferus has lateral denticles on both sides of the blade. Branson and Mehl (1934A : 
298) have reported a series of specimens which are transitional between Spatho- 
gnathodus and Pseudopolygnathus. Voges (1959 : 296, fig. 4, & 297, fig. 5) has also 
illustrated a similar transitional series in the west German Cu I faunas. 

Homoeomorphy among recurrent laterally nodose spathognathodids within the 
present fauna, is discussed below (p. 239). Thus, since the laterally nOdose spatho- 
gnathodids are homoeomorphic, and at least three chronologically distinct evolu- 
tionary lines have been demonstrated, it follows that the genus Pseudopolygnathus is 
polyphyletic. 

This can be seen in our faunas. A Lower K Zone species is known, but there is then 
a complete absence of pseudopolygnathids until the Upper Z Zone is reached in the 
North Crop, and the Lower Z Zone in the Avon Gorge. 

The Lower K Zone forms probably arose from the platform evolution of Upper 
Devonian to VI nodose spathognathodids. The Upper Z Zone forms, however, can 
be seen to have evolved directly from forms herein called S. costatus sulciferus, which 
are stratigraphically restricted to the lower and middle parts of the Z Zone. 

Homoeomorphy and taxonomy 

As in the spathognathodids, the existence of homoeomorphy in the pseudopoly- 
gnathids involves some problems in nomenclature. Since, however, most species of 
the genus were described by E. R. Branson (1934) from the Hannibal Formation of 
Missouri, in association with forms such as S. costatus sulciferus, it is probable that 



BRITISH AVONIAN CONODONT FAUNAS 201 

our upper two forms are part of the same phylogeny and should be referred to 
Branson's species, whereas the homoeomorphic Lower K Zone forms are of distinct 
origin and are best regarded as new species. 



Affinities 

Hass and others have considered that Macropolygnathus Cooper, 1939 is a junior 
subjective synonym of Polygnathus Hinde, 1879. The basal cavity of Macropoly- 
gnathus ithns, the type species of Macropolygnathus, is more akin to Pseudopoly- 
gnathus than to Polygnathus, and transitional forms have been found between M. 
ithus and P. fusiformis. We have, therefore, placed Macropolygnathus in synonomy 
with Pseudopolygnathus. 

Pseudopolygnathus is distinguished from Polygnathus by its laterally expanded 
basal cavity. 



Orientation 

In Pseudopolygnathus primus, the curvature of the longitudinal axis of the cono- 
dont and the shape of the basal cavity are bilaterally symmetrical elements. The 
ornamentation of the platform and a cross section through the blade, near the 
platform, are bilaterally asymmetrical elements. 

The inner side of the conodont is concave and the outer side is convex. Forms are 
designated as right or left, when orientated with the blade placed in front and the 
convex side to the outside. 



Posterior 



True blode 
posterior 




Outer side 



Trough 




Posterior keel 



Basal cavity 

'Lips' 
Anterior keel 



Aboral view 



Fig. 39. Pseudopolygnathus sp. showing morphological terms used in the text. 



202 BRITISH AVONIAN CONODONT FAUNAS 

THE EVOLUTIONARY DEVELOPMENT OF PSEUDOPOLYGNATHUS 

There have been three distinct developments of the genus Pseudopolygnathus in 
the Avon Gorge : one in the lower and middle parts of the K Zone, referred to as the 
Pseudopolygnathus vogesi sp. nov. development, a second near the base of Z, the 
Pseudopolygnathus primus development and a third in the upper part of the Z Zone 
the Pseudopolygnathus midtistriatus development. 

The three developments have been along similar lines, the starting point of each 
being a straight, bladed spathognathodid with lateral denticles. Specimens of 
growth series from the three developments are, with the exception of adults, 
extremely difficult to distinguish (Fig. 43). 

The evolution of pseudopolygnathus primus 

Voges (1959) noted that in the Upper Devonian the Spathognathodus costatus 
(sensu Bischoff & Ziegler) group marks the starting point in the evolutionary develop- 
ment of Pseudopolygnathus primus, and other pseudopolygnathids, which deviate 
from the typical bilateral symmetry of the spathognathodids. Voges recognized 
two groups within the Spathognathodus costatus group, right forms and left forms, the 
basal cavities of which are bilaterally symmetrical elements. The outer margin of 
the platform of right forms and the inner margin of left forms are both convex, and 
are thus bilaterally asymmetrical elements. In the left forms, there is a row of 
nodes or ridges on the inner side of the platform, which extends for three quarters the 
length of the unit. In the right forms, this row of nodes or ridges is on the outer side 
of the platform. In left forms, nodes are usually absent on the outer side of the 
platform, but in large specimens one or two nodes may be present on the outer side of 
the platform, situated near the basal cavity. Voges recognized two varieties of right 
forms, which correspond to the subspecies Spathognathodus spinulicostatus spinuli- 
costatus (Bischoff 1957) and S. spinulicostatus ultimus (Bischoff 1957). In both these 
subspecies a secondary row of nodes or small ribs extends from the middle of the 
basal cavity to the posterior extremity on the inner side of the platform. In 
Spathognathodus spinulicostatus ultimus they are more strongly developed, and a 
furrow replaces the nodes along the posterior third of the blade. 

Voges believed that S. spinulicostatus spinulicostatus and S. spinulicostatus ultimus 
were stages in the ontogenetic development of a right form, to which Spathognathodus 
costatus may be added as a left form. The opinion of Voges that S. spinulicostatus 
ultimus may represent an ontogenetic senile form of S. spinulicostatus spinulicostatus 
developed in the Wocklumeria Stage is not held by Ziegler (1962) who thinks it is 
unlikely that a fauna consisting entirely of senile members of 5. costatus (spinuli- 
costatus) spinidicostatus occurs at one horizon, while at a stratigraphically lower 
horizon, it consists entirely of non-senile members of S. costatus (spinulicostatus) 
spinidicostatus. In addition, Ziegler has found a few specimens of right forms of S. 
costatus costatus and a few left forms of S. costatus (spinulicostatus) spinidicostatus and 
5. costatus (spinulicostatus) ultimus. 

Voges believed that from the first stage, represented by the S. costatus group, there 



BRITISH AVONIAN CONODONT FAUNAS 



203 



develops a second stage, represented by Pseudopolygnathns dentilineatus (see Voges 
1959 : 297, fig. 5). In this second stage the outer margin of the platform of right 
forms and the inner margin of the platform of left forms are convex, and they are 
thus bilaterally asymmetrical elements. The outer part of the platform of left 
forms and the inner part of the platform of right forms consist of a few nodes, 
confined to the posterior part of the platforms. The basal cavities of right and left 
forms are bilaterally symmetrical elements. The two halves of the basal cavity are 
unlike in form, being characterized on the outside by a fold of the margin and a 
lip-like indentation of the edge. This form of the basal cavity is retained during 
further developments of the oral surface of the Pseudopolygnathus primus group. 

Specimens of P. dentilineatus from the P. dentilineatus development of Voges, are 
very similar to specimens of Pseudopolygnathus from the lower and middle parts of 
the K Zone of the Avonian. These specimens are here referred to as Pseudopoly- 
gnathus vogesi sp. nov. and are typical of the Cu I stage of the Sauerland (Voges 1959). 
This is the lowest development of Pseudopolygnathus in the Avonian. 

Voges was able to see the following further development of his Sauerland pseudo- 
polygnathid faunas. The nodes and ridges of the outer part of the platform in left 
forms, and on the inner part of the platform in right forms, extend towards the 
anterior end and nearer the anterior extremity of the opposite side of the platform. 
In addition, a symmetrical element is present in the ornament of the platform, when 
the inner anterior angle of the platform becomes accentuated. P. foliaceus E. R. 
Branson, and P. apetodus Cooper are representatives of this stage. 

The stage represented by P. foliaceus and P. apetodus develops into P. triangulus 
inaequalis and P. triangulus triangulus, which in the details of surface ornamentation, 
is a symmetrical element. In P. triangulus, the conspicuous asymmetry has 
disappeared and only the thickening of the blade near the platform on the right side, 
which is higher on the blade than the left, remains. 

In the uppermost part of the K Zone of the Avonian, no specimens of Pseudopoly- 
gnathus have been found. There is a second development of Pseudopolygnathus — the 
P. primus development — near the base of the Zi Limestone. The specimens of this 
development are similar, but not identical, to specimens from the stage in Voges 's 
development, which he described as including ' specimens similar to Pseudopoly- 




Fig. 40. Diagram to illustrate the ontogenetic development of pseudopolygna.thids in 

the Zi Subzone of the Avonian. 



-"» 



BRITISH AYONIAN CONODONT FAUNAS 



gnathus foliaceaus and Pseudopolygnathus apetodus '. They also closely resemble P. 
primus E. R. Branson, which occurs in the Chappel Limestone of Texas (Hass 1959). 

The starting point for the P. primus development in the Avonian are specimens 
here referred to as Spathognathodus costatus costatus, which are found in the upper 
part of the K Zone and the base of the Z Zone. Forms with a row of lateral denticles, 
here referred to as Spathognathodus costatus costatus E. R. Branson, (they are not 
identical to Spathognathodus bischoffi sp. no v., but are homoeomorphs of the latter 
species) develop a ridge on the outer side of the left forms and on the inner side of the 
right forms. The edge of the ridge becomes crenulate and, at a later stage, nodes 
develop at the posterior extremity. The next stage is marked by an increase in the 
number of nodes along the ridge towards the anterior. The anterior extremity, on 
the outer side of the left forms and on the inner side of the right forms, extends as far 
anteriorly, as it does on the inner side of left forms and on the outer side of right 
forms. A small trough is present between the carina and the nodes of the ridge on 
the outer side of right forms and on the inner side of left forms. The nodes on the 
outer side of right forms, and on the inner side of left forms, become elongated to form 
ridges in later development, as also, in further development, do the anterior nodes of 
the outer side of left forms and on the inner side of right forms. Many bizarre forms 
can be formed as a result of the thickening of the ribs, but in most adults the trough 
at the anterior extremity of the outer side of left forms and on the inner side of right 
forms can still be detected. 

A count was made of specimens of Pseudopolygnathus from a horizon 65 feet above 



4/ 4/ 4, 4/ 5/5/5/5/ 6/ & S, 6/ 7, 7. 1, 7, 8/ 8/ 8/ 8/ 

7 1 x 2 '3 <4 M x 2 7 3 x 4 A '2 7 3 '4 X 1 '2 / 3 /» M 4 ^3 X 4 



% 







NO. OF 

SPECIMENS 




-1 
-2 
-3 
-4 
-5 
-6 



4 
/ 3 



Number of nodes on right side of platform. 

Left side of the platform expanded 

Left side of the platform expanded with crenulate edge 

Left side of the platform has nodes at the posterior and a trough ot the anterior 

Left side of the platform is nodose 

Ridges on both sides of the platform. 



Fig. 41. Frequency diagram showing variation in the number of nodes and platform 
ridges in relation to platform shape in growth stages of a pseudopolygnathid population 
from a sample 65 ft. above the base of Zi in the Avon Gorge. 



BRITISH AVONIAN CONODONT FAUNAS 



205 



the base of the Zi Limestone in the Avon Gorge. The number of denticles on the 
right side ^of the platform was plotted, and also the character of the left side of the 
platform as marked by a a ridge, b a crenulated ridge, c a few denticles at the posterior 
and a trough at the anterior, or d nodes along its entire length. Adults were identi- 
fied by the presence of ridges on both sides of the platform. The results showed that 

a. Forms with 4 nodes on the right side of the platform had either a ridge, or a 

crenulate ridge on the left side of the platform. No specimens were seen which 
had 4 nodes on the right side and nodes on the left side. 

b. Forms with 5 nodes on the right side of the platform had either a crenulate ridge, 

or a few denticles at the posterior end and a trough at the anterior end. No 
specimens were found with a straight edge to the ridge, or with denticles 
continuous on the left side. 

c. Forms with 6 denticles on the right side had either a few denticles at the posterior 

extremity of the left side and a trough at the anterior extremity, or they had a 

continuous row of denticles on the left side. 
A similar plot was made of specimens higher in the section from Sample Z 21 at the 
base of Z2 (fig. 25b). In this sample fewer specimens with 4 nodes on the right side 
of the platform were present (4%, as opposed to 25% in the lower horizon.) 



Ay At Ay Ay 
'\ '2 '3 '4 



5/5/5/5, 6/6/6/6/ 7, 7, 7, 7, 

"l '2 '3 / A A '2 x 3 / A / \ '2 / 3 'A 





1 



I 



NO. OF 
SPECIMENS 

ro 



-6 



10 



y 

A 

'2 

4 

4 

7r 



Number of node* on the right side of the platform. 
Left side of the platform expanded- 

Left side of the platform expanded with a crenulate edge. 

Left side of the platform has nodes at the posterior and a trough at the anterior 
Left side of the platform is nodose. 
Ridges on both sides of the platform 



Fig. 42. Frequency diagram showing variation in the number of nodes and platform 
ridges in relation to platform shape in growth stages of a pseudopolygnathid population 
from Sample Z 21 at the base of the Z2 Subzone of the Avon Gorge. 



206 BRITISH AVONIAN CONODONT FAUNAS 

This seems to indicate that the number of denticles on the right side of the platform 
is indicative of the ontogenetic age of the specimen and that the age is also reflected 
on the left side by the stage of development, through ridge, crenulated ridge, nodose 
posterior part of ridge and a continuously nodose ridge, culminating with the 
presence of ridges on both sides of the platform. 

The stage of development in Voges's fauna represented by Pseudopolygnathus 
tricing ul us inaequalis and Pseudopolygnathus triangulus triangulus, which developed 
from the stage represented by Pseudopolygnathus foliaceus and Pseudopolygnathus 
apetodus, is not present in the Avonian. In the Avonian, specimens of Pseudopoly- 
gnathus primus are developed which consist of 7 ridges on the right side of the platform 
and a number of nodes confined to the outer margin on the left side of the platform, 
with a trough developed between the carina and the nodes of the left side of the 
platform. With further development, the nodes on the outer margin of the left side 
of the platform extend towards the carina to become ridges similar in outline to those 
on the right side of the platform. This development starts at first at the posterior 
end and extends towards the anterior, with the result that the platform on both sides 
of the carina consists of a number of ridges. The left side of the platform never 
extends as far to the anterior as the right side of the platform. In addition, a faint 
trace of a trough is present at the side of the carina, even in adult specimens. These 
forms are identical to Pseudopolygnathus multistriatus (Mehl and Thomas). 

Higher in the section forms here referred to Pseudopolygnathus cf. longiposticus 
appear and they have the same outline as advanced species of P. primus ; it is 
suggested, therefore, that they may represent a further stage in the development of 
Pseudopolygnathus. 

The third development of Pseudopolygnathus in the Avonian — P. multistriatus 
development — takes place in Z2. The specimen illustrated by Hass (1959, PI. 47, 
fig. 21) as a juvenile of Pseudopolygnathus lanceolatus is a straight-bladed spatho- 
gnathodid, with three lateral denticles. From such individuals the ontogenetic 
growth stages illustrated by Hass lead to the development of P. multistriatus. 

In juveniles (which resemble Spathognathodus tridentatus) the denticles are 
developed on one side of the platform only ; the opposite side develops at first by the 
formation of a slight ridge and, later, by the development of nodes on the ridge. A 
slight trough is again present on one side and this side is not developed as far to the 
anterior as is the other. Later development involves the replacement of nodes by 
ridges, which in adults become coarse and irregular. 

Difficulty was experienced in the present study in separating juvenile specimens of 
P. multistriatus from adult specimens of Pseudopolygnathus dentilineatus. Specimens 
in the ontogenetic sequence of P. multistriatus, which are similar to Pseudopoly- 
gnathus striatus Mehl and Thomas, are identical to P. dentilineatus of Ziegler (1962). 
Bischoff (1957) and Voges (1959) include P. striatus in synonomy with P. dentilineatus. 
In view of the fauna associated with P. striatus, including Gnathodus texanus and 
Gnathodus cuneiformis, it seems likely that Rexroad and Scott's (1964) interpretation 
in placing P. striatus in synonomy with P. multistriatus is correct. This difference 



BRITISH AVONIAN CONODONT FAUNAS 



207 



T 



Pseudopolygnathus 
multistnatus 



Pseudopolygnathus 
Pseudopolygnathus multistnatus 
multistnatus 



Spathognathodus 

costatus 
sensu ER Branson 



Pseudopolygnathus 
dentihneatus (juvenile) 

Pseudopolygnathus 

.. dentihneatus 

Pseudopolygnathus 

dentihneatus- 



Pseudopolygnathus 
primus 



Pseudopolygnathus 
vogesi. 



Spathognathodus 

spinuhcostatus 

sensu Ziegler 



Spathognathodus 

costatus 

sensu Ziegler 



Spathognathodus 
aculeatus 



Fig. 43. Phylogeny of the genus Pseudopolygnathus and related forms in the Avonian. 
Vertical lines : stratigraphic range. Full arrows : phylogenetic development. Half 
arrows : morphological variation at one horizon. 



20S BRITISH AYONIAN CONODONT FAUNAS 

in synonomy may explain the different stratigraphic ranges in North America and 
Germany for the two species in question. 

Pseudopolygnathus dentilineatus E. R. Branson 
Plate 5, figs. o,a-i3C. Plate 6, figs. 8a-c 

1934 Pseudopolygnathus dentilineata E. R. Branson : 317, PL 26, fig. 22. 
?I934 Pseudopolygnathus varicostata E. R. Branson : 318, PI. 26, figs. 19, 20. 
1934 Pseudopolygnathus subrugosa E. R. Branson : 318, PI. 26, fig. 18. 
1934 Pseudopolygnathus projecta E. R. Branson : 320, PI. 26, figs. 10, 11. 
1934 Pseudopolygnallms brevimarginata E. R. Branson : 319, PI. 26, fig. 3. 
?i939 Pseudopolygnathus varicostata E. R. Branson ; Cooper : 408-409, PI. 40, figs. 44-45. 
?i956 Pseudopolygnathus striata Mehl & Thomas ; Bischoff & Ziegler : 164, PI. 11, fig. 20. 
non 1957 Pseudopolygnathus dentilineata E. R. Branson ; Bischoff : 50, 51, PI. 4, figs. 30-32, 

( = Pseudopolygnathus vogesi sp. nov.) (PI. 4, fig. 29 = Pseudopolygnathus primus) 
non 1959 Pseudopolygnathus dentilineata E. R. Branson ; Voges : 300-301, PI. 34, figs. 49, 

50, text-fig. 511= Pseudopolygnathus vogesi sp. nov. 
non 1962 Pseudopolygnathus dentilineata E. R. Branson ; Ziegler : PI. 2, figs. 10, 11. 

Material. 182 specimens : figured, X 478, X 479, X 480, X 481, X 438, X 477. 
Range. Avon Gorge Z 12-Z 28. 

Description. This species is represented by pseudopolygnathids with an 
asymmetrical platform. Both the right and the left sides of the platform are 
ornamented with 4 to 7 nodes or ridges which are confined to the margin of the 
platform. The basal cavity is a symmetrical element, with a fold on the inner 
margin and a smooth convex outer margin in both right and left forms. The basal 
cavity, as pointed out by Klapper (1966 : 15), is as wide as the platform in aboral 
view. 

This species has bilaterally asymmetrical right and left forms. The platform is 
two and a half times as long as wide, being widest at the anterior and narrowing to 
the pointed posterior. In adult specimens the platform is less triangular and more 
oval in outline. The margin of the right side of the platform in both right and left 
forms is convex and widest at mid-length : that of the left side of the platform is 
widest close to the anterior and narrows to the pointed posterior. The right side of 
the platform in both right and left forms extends further to the anterior than does the 
left side. The platform on either side of the carina is ornamented by 4 to 7 nodes or 
ridges, which are confined to the margin. There is usually one more node present on 
the right side of the platform than on the left. In smaller specimens a distinct 
trough may be present between the denticles of the margin and the carina, in the 
anterior half of the left side of the platform. A central straight to slightly curved 
nodose carina runs the length of the platform. The nodes of the anterior portion of 
the carina are stubby and wider than those of the posterior, which are more distinct 
and erect. The carina in smaller specimens extends a short distance beyond the 
posterior extremity of the platform. 

The anterior blade, commonly composed of 6 denticles, is highest at the anterior 
end and slopes uniformly to the posterior. 



BRITISH AVONIAN CONODONT FAUNAS 209 

In aboral view the basal cavity is large and occupies the anterior half of the 
platform ; the outer side of the margin has a slight fold. The basal cavities of right 
and left forms are bilaterally symmetrical elements. 

Remarks. In the basal beds of the Z Zone specimens of P. primus occur, which 
resemble P. dentilineatus in outline, but which differ in detail because the nodes or 
ridges of the right side of the platform are not confined to the margin, as in P. 
dentilineatus, but are elongated and extend into the carina. Also in adult P. primus 
there is a greater number of ridges than in adult P. dentilineatus. The anterior 
trough on the left side of the platform is present in both P. dentilineatus and P. 
primus, but in the latter species the nodes at the posterior of the left side of the 
platform are extended to the carina and form ridges. In addition the basal cavity is 
as wide as the platform in P. dentilineatus, but less wide in P. primus. 

Higher in the section, forms resembling P. dentilineatus are found, but it is thought 
that they represent growth stages of other pseudopolygnathids. P. striatus Mehl and 
Thomas, for example, is similar to P. dentilineatus but can be shown by ontogenetic 
studies to be a growth stage of P. multistriatus. 

We agree with Klapper (1966 : 15) that P. dentilineatus developed from double 
rowed forms of Spathognathodus. We do not regard S. costatus ultimus as their direct 
ancestor. 

Pseudopolygnathus expansus sp. nov. 
Plate 5, figs. 2a-c, 4a-c 

Derivation of name. After the expanded anterior part of the platform. 

Diagnosis. Pseudopolygnathid with straight axis in the mid and anterior thirds, 
but curved in the posterior third. Anterior third of the right platform is expanded. 
Outer margin, except expanded part, has convex outline and is ornamented by nine 
or more transverse ridges. Anterior to mid length of unit, margin of inner side of 
platform is expanded for a short distance. Basal cavity is asymmetrically flared ; 
both inner and outer anterior margins of basal cavity expanded laterally, but that of 
outer margin is greater. 

Material. 3 specimens : Holotype X 483, Paratype X 482 (both figured). 

Type locality and horizon. Avon Gorge, the middle of the K Zone. Sample 
K 12. 

Range. Avon Gorge, K 12. 

Description. The platform is lanceolate in outline. The axis of the unit is 
straight in the mid and anterior thirds, but curved in the posterior third. The 
platform is widest anterior to mid-length and is two to three times as long as wide. 
The convex margin of the outer side of the platform is interrupted by a lateral 
expansion of the platform, mid-way between the anterior edge and the mid-length of 
the unit. The outline of the inner margin posterior to the mid-length is straight to 
slightly convex. At the mid-length the inner platform is expanded and tapers 
gradually from the expanded portion to the anterior extremity. The outer side of 
the platform is ornamented by up to nine transverse ridges, extending from the 



.mo BRITISH AVONIAN CONODONT FAUNAS 

margin to the carina. The inner side of the platform is ornamented by up to eleven 
ridges, the posterior two being nodose at the margin ; the ridges in the posterior half 
of the inner platform extend to the carina from the margin. Those of the anterior 
half do not reach the carina and a trough is present, which is open to the anterior. 
The anterior edge of the inner part of the platform is lower on the carina than is the 
anterior edge of the outer part of the platform, which is at the same level as the 
carina. The 4 posterior denticles of the carina are nodose, but the remainder of the 
carina is composed of fused denticles. 

The basal cavity is asymmetrical, pointed posteriorly and rounded anteriorly. 
Both the inner and outer margins of the basal cavity are expanded laterally in the 
anterior half. The anterior blade is of unknown form. 

Remarks. Pseudopolygnathus expansus sp. nov. is closely related to Pseudopoly- 
gnathus vogesi sp. nov. and transitional specimens have been found (PI. 5, fig. 6-7), but 
is distinguished from it by the expanded anterior portion of the outer side of the 
platform. In this respect it resembles P. primus and is interpreted here as a homoeo- 
morph of the latter species. 

Pseudopolygnathus cf. fusiformis Branson & Mehl 

Plate 6, fig. 1 

1934 Pseudopolygnathus fusiformis Branson & Mehl : 298, PI. 23, figs. 1-3. 

Material, i specimen : figured, X 552. 

Range. Avon Gorge, C 14. 

Description. A narrow platform is developed on either side of the strongly 
denticulate carina. The platform is widest anteriorly and tapers uniformly to the 
pointed posterior. In lateral view the platform is arched. The margins of the 
platform are notched and edged by 5 or 6 nodes. The blade is almost as long as the 
platform, and contains 7 denticles, which are fused with the high denticles of the 
carina. The carina is continued a short distance beyond the posterior extremity and 
bears 2 or 3 denticles. Aborally, there is a large basal cavity, typical of Pseudopoly- 
gnathus, which extends anteriorly to the junction of the blade and platform. It is 
rounded anteriorly and pointed posteriorly. 

Remarks. The specimen most closely resembles Pseudopolygnathus fusiformis 
Branson & Mehl, but it may be a juvenile of Polygnathus. 

Pseudopolygnathus cf. longiposticus Branson & Mehl 

Plate 30, figs. 3, 7, 9-17 

1934 Polygnathus longipostica Branson & Mehl : 294, 311, PI. 24, figs. 8-11. 

Material. 107 specimens : figured, X 522, X 523, X 433, X 434, X 545, X 442, 
X 443, X 448, X 449, X 547. 

Range. Avon Gorge Z 11-C 7. 



BRITISH AVONIAN CONODONT FAUNAS 211 

Description. The unit is straight, the platform being about twice as long as the 
blade. It is widest near mid-length and tapers to the posterior. The central carina 
is nodose and is continued a short distance beyond the posterior edge. One of the 
nodes of the carina near the posterior is higher than the others. The platform is 
ornamented by a number of short ridges near the outer margin, normal to the 
carina. The troughs between the carina and the ridges are unornamented. The 
anterior blade is high and composed of 5 fused denticles. In lateral view this species 
has a characteristic outline. The oral edge is highest at the anterior and slopes 
regularly to the posterior. The oral edge of the platform is arched convexly. The 
aboral edge is strongly concavely arched. In aboral view there is a very large pit 
and a strong keel. 

Remarks. The present specimens, although very close to P. longiposticus, differ 
in the outline of the platform, which more closely resembles that of Polygnathus 
macrus Cooper and Polygnathus orthus Cooper. 

Pseudopolygnathus multistriatus Mehl & Thomas 
Plate 5, figs. 14-16. Plate 6, fig. 2 

1947 Pseudopolygnathus multistriata Mehl & Thomas : 16, PI. 1, fig. 36. 

1947 Pseudopolygnathus attenuata Mehl & Thomas : 17, PI. 1, fig. 9. 

1947 Pseudopolygnathus rustica Mehl & Thomas : 17, PI. 1, fig. 8. 

1947 Pseudopolygnathus striata Mehl & Thomas : 17, PI. 1, fig. 10. 

1957 Pseudopolygnathus multistriata Mehl & Thomas ; Bischoff : 51, PI. 4, figs. 33, 35. 

I 959 Pseudopolygnathus lanceolata Hass : 391, PI. 47, figs. 16—26. 

1964 Pseudopolygnathus multistriata Mehl & Thomas ; Rexroad & Scott : 41, 42, PI. 2, 
fig- 30- 

Material. 46 specimens : figured, X 485, X 486, X 487, X 484. 

Range. Avon Gorge Z 23-Z 29. 

Description. This species is distinguished by the platform, which is not 
markedly asymmetrical ; it is ornamented by transverse ridges, usually nine or more 
on either side of the central carina. There is a short anterior blade, and a trough on 
the side of the carina in the anterior part of the left side of the platform. Adult 
specimens frequently have rough oral surfaces owing to the coarse nature of the 
ornament. 

The platform is three and a half times as long as wide and has convex margins. 
The axis is straight to slightly curved and the platform on the left side of the carina 
does not extend as far to the anterior, as does the platform on the right side. The 
platform on either side of the carina is ornamented by 9 nodes which elongate into 
ridges reaching the carina. A slight trace of a trough is, however, present in the 
anterior part of the left side of the platform. The anterior two thirds of the carina 
is composed of fused denticles, but in the posterior third the denticles of the carina 
are free and distinct. The carina is continued a short distance beyond the posterior 
extremity of the platform. The anterior blade, composed usually of 5 denticles, is 
highest at the anterior and decreases in height to its junction with the carina. The 



2i2 BRITISH AVONIAN CONODONT FAUNAS 

anterior blade is also equal in height to its length, and is curved in the opposite 
direction to the curvature of the posterior extension of the carina. The basal cavity, 
situated in the anterior part of the unit, is subcircular in outline, but more drawn out 
to the posterior than the anterior. It is as wide as the platform in juveniles, but in 
adults is less wide than the platform. 

Remarks. This species developed from Pseudopolygnathus primus by the extension 
of the nodes on the left side of the platform towards the anterior, and by a change in 
the platform ornament from marginal nodes to transverse ridges. 

Pseudopolygnathus striatus, P. rusticus, P. attenuatus and P. lanceolatus are all 
considered to be growth stages of P. multistriatus. P. striatus is a homoeomorph of 
P. dentilineatus, as pointed out by Klapper (1966 : 15). 

Lower Z forms referred to P. dentilineatus in this study (PI. 6, fig. 8) resemble P. 
multistriatus (PI. 5, fig. 16), but the left side of the platform is more strongly 
developed, and also there are 8 nodes or ridges on the right side of the platform in 
P. multistriatus. 

The Avonian P. multistriatus pseudopolygnathids gave rise to P. cf. longiposticus. 

Pseudopolygnathus nodomarginatus (E. R. Branson) 
Plate 9, figs. ia-4c. Plate 12, figs. 6a-8c, ioa-c 

1934 Polygnathus nodomarginata E. R. Branson 310, PI. 25, fig. 10. 

1934 Pseudopolygnathus brevimarginata E. R. Branson 322, PI. 26, fig. 3. 

1934 Pseudopolygnathus tenuis E. R. Branson 319, PI. 26, figs. 13, 14. 

1938 Polygnathus flabella Branson & Mehl : 147, PI. 34, fig. 48. 

!939 Polygnathus anida Cooper : 399, PI. 39, figs. 39, 40. 

x 939 Polygnathus flabellum Branson & Mehl ; Cooper : 400, PI. 39, figs. 13, 14. 

1944 Polygnathus flabella Branson & Mehl ; E. B. Branson : 208, 221, PI. 39, fig. 48. 

1949 Polygnathus anida Cooper ; Thomas : 411, PI. 3, figs. 10, 11. 

1950 Streptognathodus ? sp. Youngquist, Miller & Downs : 529, PI. 67, figs. 12-14. 

195 1 Polygnathus aff. symmetrica Branson & Mehl ; Youngquist & Downs : 789, PI. 111, 
fig. 6. 

1956 Polygnathus inornata E. R. Branson ; Bischoff & Ziegler : 157, PI. 12, figs. 4, 5. 

1957 Polygnathus nodomarginata E. R. Branson ; Bischoff & Ziegler : 157, PI. 12, fig. 6. 
J 959 Polygnathus cf. flabellum Branson & Mehl ; Voges : 290, PI. 34, figs. 8-1 1. 

non 1959 Polygnathus nodomarginata E. R. Branson ; Helms : 251, PI. 3, figs, ia, b, c. 
1966 Polygnathus nodomarginata E. R. Branson ; Jones & Druce : 358, fig. 3, No. 3. 

Material. 323 specimens : figured, X 488, X 489, X 490, X 491, X 492, X 493, 
X 494, X 495. 

Range. North Crop ZLA 29-ZL 18. 

Description. The platform is asymmetrical, one side being shorter than the 
other. In juveniles it is ornamented by a lateral row of nodes on each margin with a 
trough on either side of the medial carina (PI. 9, fig. 1) . With old age the rows of nodes 
expand into a platform with transverse ridges and the troughs tend to shallow (e.g. 
PI. 12, fig. 6a). The carina is coarsely nodose and extends posteriorly, the juveniles 
often exhibiting a longer posterior free blade than the adults. The anterior blade is 
about half the platform length ; the highest denticles are developed anteriorly and 



BRITISH AVONIAN CONODONT FAUNAS 213 

are just higher than the highest point of the platform in lateral view ; the blade is 
made up of 7 to 8 fused, laterally compressed, denticles. 

In aboral view the basal cavity is lanceolate, being widest at the anterior end of the 
platform and narrowing gradually toward the posterior, where it becomes a narrow 
groove in a deep keel. 

Remarks. It appears that this species is closely related to P. lacinatus, the 
platform ornament serving to distinguish them. 

The most distinctive features of the present species are its more or less laterally 
expanded basal cavity, its relatively strong ornament, and its relatively long blade. 
The platform ranges from elongate pointed to broadly lanceolate in oral outline. 

It is difficult to decide whether this species is better assigned to the genus Pseudo- 
polygnathus or to the genus Polygnathus, but because some specimens possess typical 
pseudopolygnathid cavities, it is here included in this genus. 

Pseudopolygnathus postinodosus sp. nov. 
Plate 6, figs. 6a-c 

Derivation of name. After the high denticles of the posterior extension of the 
carina. 

Diagnosis. Pseudopolygnathus characterized by posterior extension of carina 
bearing a few high denticles. Platform situated in mid-third of unit bears a few 
indistinct nodes confined to convex margins. Anterior blade also distinctive, being 
highest at mid length, sloping abruptly to posterior and more gently to anterior. 
Basal cavity elongate with thickened lips. 

Material. 3 specimens : Holotype X 496 (figured). 

Type locality and horizon. Avon Gorge Z2 Limestones. Sample Z 38. 

Range. Avon Gorge Z 13-Z38. 

Description. In oral view the platform is seen to occupy the mid third of the 
unit, the anterior blade the anterior third of the unit, and the posterior extension of 
the carina the posterior third. The axis is straight to slightly curved and it is 
possible to recognize right and left forms, although in the present study only right 
forms have been found. The anterior blade is composed of 7 denticles ; the 3 at the 
posterior are smaller than the other 4. The fourth anterior denticle is highest and 
the third anterior denticle is only slightly lower than the fourth. The anterior two 
denticles are, like the third and fourth, free for the greater part of their length, but 
they are lower than the third and fourth denticles. The carina in the region of the 
platform is low and consists of a number of stubby denticles, which are fused together. 
At the posterior extremity of the platform the denticles of the carina become distinct, 
and on the posterior extension there are a few distinct high denticles. 

In lateral view the denticles of the anterior blade and of the posterior extension of 
the carina are stout and spine-like. The three denticles of the posterior extension of 
the carina are free from the base to the tips, and diverge at a wide angle from one 
another. The anterior edge of the anterior blade and the posterior edge of the 



2i 4 BRITISH AVONIAN CONODONT FAUNAS 

posterior extension of the carina are of equal elevation. The four high anterior 
denticles of the anterior blade give the anterior edge of the anterior blade a serrated 
appearance. The low carina is raised slightly above the level of the platform. 

The basal cavity is situated in the anterior part of the platform. It has an oval 
outline, with very thick lips. It is slightly longer than wide and a narrow trough 
runs from the pit to the posterior extremity of the platform. A keel runs from the 
anterior extremity of the basal cavity to the anterior extremity of the unit. 

Remarks. It is considered likely that Pseudopolygnathus postinodosus sp. nov. 
developed from Spathognathodus sp. nov. by the continued development of a platform, 
transitional specimens between the two species having been found. In these transi- 
tional specimens a second row of nodes is developed on the inner side of the blade, 
directly over the basal cavity. This development is in addition to the row of nodes 
on the outer side of the blade (see Fig. 47). 

Pseudopolygnathus primus Branson & Mehl 
Plate 6, figs. 4a-5c, 7ioa-i2c 

1934 Pseudopolygnathus prima Branson & Mehl : 298, PI. 24, figs. 24, 25. 

1934 Pseudopolygnathus foliacea E. R. Branson : 316, PI. 26, figs. 27, 28. 

1934 Pseudopolygnathus irregularis E. R. Branson : 316, PL 26, figs. 25, 26. 

1934 Pseudopolygnathus corrugata E. R. Branson : 317, PI. 26, fig. 23. 

1934 Pseudopolygnathus costata E. R. Branson : 317-318, PI. 26, fig. 21. 

1934 Pseudopolygnathus distorta E. R. Branson : 318-319, PL 26, figs. 16, 17. 

? 1934 Pseudopolygnathus varicosiata E. R. Branson : 318, PL 26, figs. 19, 20. 

1934 Pseudopolygnathus sulcifera E. R. Branson : 319, PL 26, fig. 15. 

1934 Pseudopolygnathus asymmetrica E. R. Branson : 320, PL 26, fig. 12. 

1934 Pseudopolygnathus inequicostata E. R. Branson : 321, PL 26, fig. 6. 

1934 Pseudopolygnathus crenulata E. R. Branson : 321, PL 26, figs. 4, 5, 7, 8. 

1934 Pseudopolygnathus lobata E. R. Branson : 322, PL 26, figs. 1, 2. 

1938 Pseudopolygnathus prima Branson & Mehl ; Branson & Mehl : PL 33, figs. 47, 48. 

? 1938 Pseudopolygnathus varicostata E. R. Branson ; Branson & Mehl : 133, PL 33, figs. 25, 
46. 

1939 Polygnathus subserrata Branson & Mehl ; Cooper : 404, PL 39, figs. 75, 76 only. 

J 939 Pseudopolygnathus asymmetrica E. R. Branson ; Cooper : 406-407, PL 40, figs. 23, 24, 
59, 60, PL 41, figs. 13, 14. 

1939 Pseudopolygnathus crenulata E. R. Branson ; Cooper : 407, PL 40, figs. 25-27. 

? 1939 Pseudopolygnathus varicostata E. R. Branson ; Cooper : 408, PL 40, figs. 44, 45. 

1939 Pseudopolygnathus prima E. R. Branson & Mehl ; Cooper : 408, PL 40, figs. 30, 31. 

!939 Pseudopolygnathus irregularis Branson ; Cooper : 408, PL 40, figs. 21, 22, 35, 36. 

J 939 Pseudopolygnathus distorta E. R. Branson ; Cooper : 408-409, PL 40, figs. 49-50. 

1944 Pseudopolygnathus prima Branson & Mehl ; Branson & Mehl : 244, PL 94, figs. 11, 12. 

1944 Pseudopolygnathus prima Branson & Mehl ; Branson & Mehl : 181, PL 32, figs. 25, 26. 

? 1944 Pseudopolygnathus varicostata E. R. Branson ; Branson & Mehl : 181, 222, PL 32, 
figs. 25, 46. 

1949 Pseudopolygnathus aurita Youngquist & Patterson : 67-68, PL 16, figs. 5, 6. 

1949 Pseudopolygnathus carinata Youngquist & Patterson : 68, PL 16, fig. 4. 

1949 Pseudopolygnathus irregularis Branson ; Youngquist & Patterson : 68-69, PL 16, 

figs- i-3- 
1949 Pseudopolygnathus prima Branson & Mehl ; Thomas : 412, PL 4, fig. 17. 



BRITISH AVONIAN CONODONT FAUNAS 215 

1949 Pseudopolygnathus cf. crenulata E. R. Branson ; Thomas : 412, PL 4, fig. 18. 

1949 Pseudopolygnathus constrictiterminata Thomas : 428, PI. 4, fig. 16. 

1949 Pseudopolygnathus cf. P. asymmetrica E. R. Branson ; Thomas : 436, PI. 3, fig. 42. 

195 1 Pseudopolygnathus prima Branson & Mehl ; Hass : 2358, PI. 1, fig. 11. 

1957 Pseudopolygnathus prima Branson & Mehl ; Cloud, Barnes & Hass : 813, PI. 5, fig. 10. 

1957 Pseudopolygnathus irregularis Branson ; Bischoff : 51, PI. 6, figs. 12, 13. 

1957 Pseudopolygnathus dentilineata E. R. Branson ; Bischoff : 50, 51, PL 4, fig. 29 only. 

*959 Pseudopolygnathus prima Branson & Mehl ; Hass : PL 49, fig. 27. 

J 959 Spathognathodus cf. costatus (E. R. Branson) Voges : 298, 299, PL 34, fig. 48 only. 

1966 Pseudopolygnathus prima Branson & Mehl ; Klapper : 14, PL 4, fig. 8. 

Material. 64 specimens : figured, X 546, X 497, X 498, X 499, X 500, X 549. 

Range. Avon Gorge Z 13-Z 28. 

Description. This species is extremely variable. All forms with an asym- 
metrical platform, a narrow row of nodes or ridges on the right and left sides, but 
with a flared anterior portion on the left, are referred to it. The basal cavity, accord- 
ing to Klapper, is narrower than the platform, but not all our specimens of P. primus 
agree with this. 

The axis is arched, and right and left forms have been found which are bilaterally 
asymmetrical elements. The platform is more strongly developed on the right side 
than on the left in both right and left forms. The outer margin of the right side of 
the platform is convexly curved and bears at least 7 nodes or ridges. The right side 
of the platform is widest at mid-length, and tapers uniformly to the anterior and 
posterior. The shorter left side of the platform consists of a smaller number of 
nodes or ridges than the right side. The carina consists of fused denticles for the 
greater part of its length, but there are a few distinct denticles at the posterior 
extremity, where the carina is extended a short distance beyond the posterior end of 
the platform. 

The basal cavity is situated near the mid third of the unit, and is sub-circular in 
outline with a fold on the inner margin and with a convex outer margin. A narrow 
groove extends from the anterior extremity of the basal cavity to the posterior 
extremity of the unit. The anterior edge of the unit, anterior to the basal cavity, 
is sharp. 

Remarks. Pseudopolygnathus primtis is similar in outline to P. dentilineatus, but 
the platform ornamentation in the two species is different. The platform ornamen- 
tation of P. primus has at least seven nodes or ridges on the right side, and ridges are 
frequently present, whereas in Pseudopolygnathus dentilineatus there are nearly always 
nodes which are confined to the margin ; ridges are rare and eight nodes or ridges on 
the right side of the platform are unknown. Both margins of the platform in P. 
dentilineatus are convex. In P. primus the margin of the left side of the platform is 
more angular at the anterior than that of P. dentilineatus. 

The development of P. primus has been described by Voges (1959) and again by 
Klapper (1966). The writers agree with the opinion of Klapper (1966 : 14) that 
there is a wide variety of surface ornamentation in P. primus, but that this can be 
regarded as intraspecific variation. 



216 BRITISH AVONIAN CONODONT FAUNAS 

P. primus developed from P. dentilineatus in the Avonian. Three morphological 
variations of P. primus have been observed : those with a wing-like expansion at 
the anterior (PI. 6, fig. 10), those with a considerably larger right side to the platform 
(PI. 6, fig. 7) and those where there is a distinct trough on the left side of the anterior 
part of the platform (PI. 6, figs. 11, 12). This latter variation closely resembles P. 
multistriatus and becomes the dominant form of P. primus in the middle part of the 
Z Zone. 

Pseudopolygnathus triangulus cf. pinnatus Voges 
Plate 30, fig. 19 

*959 Pseudopolygnathus triangula triangula Voges : 304, 305, PI. 35, figs. 7-13, p. 297, text-fig. 

5 IV. 
1963 Pseudopolygnathus triangula subsp. indet Voges ; Ziegler : PI. i, figs. 1, 2. 
1963 Pseudopolygnathus triangula triangula Voges ; Ziegler : PI. 1, figs. 3, 4. 

Material. 3 specimens : figured, X 502. 
Range. Avon Gorge C 7. 

Description. This species is characterized by having a platform with a triangular 
outline. It is straight and wide at the anterior edge of the platform. The platform 
in oral view is widest slightly anterior to its mid-length. It tapers gradually to the 
posterior, having straight margins and a triangular posterior outline. Anterior to 
the mid-length, the margin of the platform is gently curved and it tapers suddenly 
to the anterior. The anterior blade is broken. The platform is one and a half times 
as long as wide and has a straight axis. The oral surface of the platform is flat to 
slightly concave and is ornamented by a number of ridges normal to the margin, 
which are confined to the outer half of the platform and do not reach the carina. 
The central carina is strongly developed and has knob-like projections on its upper 
surface. 

The aboral surface is flat and wide. The margins of the outer position are slightly 
upturned. A strong keel runs the length of the unit, interrupted by the small 
anteriorly situated pit of the basal cavity. 

Remarks. The specimens found in the present study most closely resemble 
Pseudopolygnathus triangula subsp. indet Ziegler (1963), but the anterior edge of the 
platform is neither as straight nor as wide as it is in the type specimen (Voges 1959). 
The present specimens have a more rounded anterior extremity. 

Pseudopolygnathus vogesi sp. nov. 
Plate 5, figs, ia-c, 3a-c, 5a-8 

?i956 Pseudopolygnathus striata Mehl & Thomas ; Bischoff & Ziegler : 164, PI. 11, fig. 20. 
?I957 Pseudopolygnathus dentilineata E. R. Branson ; Bischoff : 50, 51, PI. 4, figs. 30, 31, 

32 only, (non PI. 4, fig. 29 = Pseudopolygnathus primus). 
?I959 Pseudopolygnathus dentilineata E. R. Branson ; Voges : 297, text-fig. 5, fig. II, PI. 34, 

figs- 49. 50. 
?ig64 Pseudopolygnathus sp. Bouckaert & Ziegler : 27, PI. 4, fig. 12. 



BRITISH AVONIAN CONODONT FAUNAS 217 

Derivation of name. After Dr. A. Voges. 

Diagnosis. Pseudopolygnathid with triangular platform, widest anteriorly, 
tapering uniformly to pointed posterior. Usually 5 non-marginal bulbous nodes on 
one side of the platform, and six on the other, confined to the margin. Carina 
straight or slightly curved, bearing nodes fused towards anterior and free towards 
posterior. Asymmetrical basal cavity occupying anterior half of platform has fold 
developed on inner side of unit. Blade low and about equal in length to platform. 

Material. 56 specimens : Holotype X 155, Paratype X 504, X 501, X 505, 
X 507, X 506 (all figured). 

Type locality and horizon. Avon Gorge, lower and middle part of the K Zone. 
Sample K 12. 

Range. Avon Gorge K 4-K 14, North Crop KL i-KL 5. 

Description. The axis of the unit is straight or slightly curved. The carina 
consists of 12 or more nodes, which are fused at the anterior and free at the posterior 
end. The platform, which is two and a half times as long as its maximum width, is 
widest anteriorly, there being an abrupt taper to the anterior extremity of the 
platform. The margins are slightly convex in the anterior third and taper uniformly 
to the pointed posterior. The posterior tip of the carina continues a short distance 
beyond the posterior extremity of the platform. The outer side of the platform 
extends slightly further to the anterior and is also slightly narrower than the other 
side. It bears up to 5 bulbous nodes, which extend from the margin to the carina ; 
the central node is widest and the anterior two are bigger than the posterior two. 
The inner side of the platform has up to 6 bulbous nodes, which are smaller than 
those of the opposite side of the platform. The anterior four nodes do not extend 
to the carina and are confined to the margin. As a result, there is an anterior trough 
present in the anterior part of the platform. 

The outer side of the asymmetrical basal cavity is convex and the inner side has a 
fold in the anterior part. The basal cavity is wide and occupies the anterior half of 
the aboral surface. It is pointed posteriorly and rounded anteriorly. The anterior 
blade consists of 5 or 6 denticles which are highest at mid-length. 

Remarks. P. vogesi occurs in the lower and middle parts of the K Zone in the 
Avon Gorge. It is a homoeomorph of ' Pseudopolygnathus dentilineata ' E. R. 
Branson. It resembles P. dentilineatus as illustrated by Voges (1959 : 297, text- 
fig. 5, n) which is characteristic of the lower part of Cu I in West Germany (Bischoff 
1957, Voges 1959) and Pseudopolygnathns n. sp. of Bouckaert & Ziegler (1965 : 27, 
PI. 4, fig. 12). In North America, the lowest stratigraphic occurrence of the genus 
Pseudopolygnathus in the Mississippian is the occurrence of P. dentilineatus at the 
base of the Glen Park Formation. P. dentilineatus ranges into the lower and middle 
part of the Hannibal Formation in the Mississippi Valley (Collinson, Scott & Rexroad 
1962). 

Pseudopolygnathus vogesi sp. nov. is similar to P. expansus sp. nov. and transitional 
specimens have been found. 



218 BRITISH AVONIAN CONODONT FAUNAS 

Pseudopolygnathus sp. A 
Plate 6, fig. 3 

Material. 6i specimens : figured, X 515. 

Range. North Crop ZLA 29-ZLA 32. 

Description. The specimen illustrated is very long and narrow. The platform 
is extremely variable in its development and always highly irregular in outline. 
Often it consists of irregular nodes rising out of the thickened medial part of the 
unit ; sometimes these are fused to give a nodose platform of 3 to 4 denticles on 
either side of the carina. Occasionally there are no nodes on the medial thickening. 
The carina is very distinctive, consisting of sub-circular needle-like denticles standing 
high above the platform. The anterior blade is very long and is a continuation of 
the carina. In aboral view the basal cavity is elongate and asymmetrically flared. 

Genus SCAPHIGNATHUS Ziegler i960 
i960 Scaphignathus Ziegler : 403. 

Type species. Scaphignathus velifera Ziegler i960. 

The generic name and the type species were used, and the latter described, by 
Helms (1959 : 655) who referred both to Ziegler 1959 as author. Ziegler's paper was 
not published until i960, but subsequent authors have also attributed the genus to 
him, and we follow this practice, which Article 50 of the Code of Zoological Nomen- 
clature clearly allows. 

Scaphignathus ? sp. A 
Plate 2, figs. I3a-c 

Material, i specimen : figured, X 532. 

Range. North Crop ZL 2. 

Description. The unit is boat-shaped, being asymmetrical with the anterior 
blade developed on the right hand side when viewed posteriorly. The anterior blade 
is broken in the only specimen. The platform is lanceolate, being widest at the 
anterior, and is triangular in cross-section in the posterior portion. It is over twice 
as long as wide, and is ornamented with low transverse ridges, terminating in low 
nodes on the platform edge. Along the mid-line there runs a low nodose carina, 
which joins the inner edge immediately posterior to the outer lateral blade, and then 
runs as a low ridge anteriorly, joining the outer lateral blade and thus preventing the 
trough from opening anteriorly. 

In aboral view the cavity is large and asymmetrical, being expanded on the inner 
side : the posterior part of the platform has a keel with a median groove. 

Remarks. This form differs from Scaphignathus ? sp. B in that the oral trough 
does not open anteriorly. The reasons for placing these two forms tentatively in the 
genus Scaphignathus are given in the remarks following the description of S. sp. B. 



BRITISH AVONIAN CONODONT FAUNAS 



219 



Platform 
Carina \ 


Blade 
1 Anterior 


Posterior J^tCjiS » W /jjtlfc j 


W^ffffif^nh^' 


Outer side 


Ridges 




Oral view 




Oral edge A 




Platform_j£sSS^.s^.-^^s5; 
Posterior ^^K*S^' '{%£/ % 


'!.' '•'.' A Anterior 
£^/-**3*«lade 


Aboral edge 

Lateral view 





Fig. 44. Scaphignathus sp. showing morphological terms used in the text. 

Scaphignathus ? sp. B 
Plate 2, figs. i2a-c 

Material. 3 specimens : figured, X 533. 

Range. North Crop ZL 9-ZL 10, Avon Gorge Z 12. 

Description. The only specimens present in our faunas have the posterior part 
of the platform missing. The blade consists of 5 denticles of equal height, situated 
on the right side of the platform when viewed from the posterior. The outer 
platform ornament consists of low transverse ridges, giving a crenulate platform, 
uniting with the inner side immediately posterior to the outer anterior blade, and 
running as a low, non-denticulate inner blade not quite to the anterior of the unit. 
It is separated from the outer lateral blade by a sulcus, which deepens anteriorly. 

In aboral view the cavity is large and asymmetrical, being expanded on the inner 
side. The unit is sub-triangular in cross-section and essentially boat-like. 

Remarks. The presence of a median carina precludes the placing of these two 
species in either Cavusgnathus or Clydagnathus and the basal cavity differs greatly 
from the small basal cavity of Mestognathus. Scaphignathus has a small pit in adult 
specimens but a large one in juveniles. Our specimens would appear to be adult but 
are tentatively assigned to that genus. 



Genus SIPHONODELLA Branson & Mehl 



1934 Siphonognathus Branson & Mehl : 295 (non Richardson 1858). 
1944 Siphonodella nom. nov. Branson & Mehl : 245. 

Type species. Siphonognathus duplicata Branson & Mehl 1934. 



22o BRITISH AVONIAN CONODONT FAUNAS 

Siphonodella isosticha (Cooper) 
Plate 12, figs. 9a, b, 11a, b 

1930 Siphonognathus isosticha Cooper : 409, PI. 41, figs. 9, 10. 

1962 Siphonodella n. sp. A Collinson, Scott & Rexroad : 7, fig. 4. 

1962 Siphonodella obsoleta Cooper ; Miiller (partim) : 1388, fig. 4 only. 

1964 Siphonodella isosticha (Cooper) Rexroad & Scott : 44, PI. 3, figs. 21-23. 

1965 Siphonodella isosticha (Cooper) Ethington : 587, PI. 67, figs. 15, 17, 

Material. 3 specimens : figured, X 534, X 535. 

Range. North Crop KL 16-KL 19. 

Description. The platform is narrow and elongate being broadest at its mid- 
point. Ornament is lacking except for a medial nodose carina, two short anterior 
rostral ridges, a few scattered nodes on the narrow inner platform, and incipient 
transverse denticles on the margin of some specimens (PI. 12, fig. 11a). The basal 
cavity is minute, and the whole unit keeled. 

Remarks. Rexroad & Scott (1964 : 44) suggested that this species arose from 
5. obsoleta Hass by reduction of the outer rostral ridge and platform ornament, but 
they pointed out that the juveniles of the two species are very similar. All our 
specimens appear to be young forms and they could be assigned either to S. obsoleta 
or 5. isosticha, but absence of platform ornament in the largest specimen suggests 
that they should be placed in S. isosticha. 

Siphonodella obsoleta Hass 
Plate 12, figs. I3a-c 

J 959 Siphonodella obsoleta Hass : 392, PI. 47, figs. 1, 2. 

1962 Siphonodella aff. S. obsoleta Hass ; Collinson, Scott & Rexroad : 7, chart 2. 
1964 Siphonodella obsoleta Hass ; Rexroad & Scott : 45, PI. 3, fig. 25. 

1964 Siphonodella obsoleta Hass [Nass in text] ; Budurov & Tschurnev : PI. V, figs. 5a-c, 
11a, b, 13a, b, 14-17, 19. 

Material. 2 specimens : figured, X 536. 
Range. North Crop KL 16-KL 19. 



Posterior 




Platform 

Loteral ridges 

Outer side 

Rostrol ridge 



A ntenor blade 



Fig. 45. Siphonodella sp. showing morphological terms used in the text. 



BRITISH AVONIAN CONODONT FAUNAS 221 

Description. The long outer rostral ridge distinguishes this species from S. 
isosticha (Cooper). The ridge is situated on the outer platform and curves away 
from the carina, paralleling the platform margin. It degenerates into a line of low 
isolated nodes before becoming obsolescent near the posterior termination. The 
inner platform bears irregular low nodes over the whole surface. 

Siphonodella sp. A 
Plate 12, figs. 12a, b 

Material, i specimen : figured, X 537. 
Range. North Crop KL 16. 

Description. This specimen is a siphonodellid with a rounded posterior margin, 
and a lobe developed on the posterior part of the outer side. The inner platform 
possesses two longitudinal rostral ridges in its anterior part, the posterior part being 
expanded laterally and ornamented with irregular low nodes, three of which replace 
the carina, while others spread on to the outer platform. The outer platform 
possesses a long rostral ridge, which covers the length of the platform and extends 
along a lobe situated in the posterior part. The platform is unornamented except 
for isolated nodes in the posterior. 

In aboral view the unit is relatively flat and possesses a minute siphonodellid 
cavity. 

Remarks. This specimen is unlike any other described siphonodellid species. It 
may be a pathologic variant of S. obsoleta Hass. 

Siphonodella sp. 
Plate 31, fig. 20 

Material. 2 specimens : figured, X 539. 

Range. Avon Gorge K 12-K 17. 

Description. Two fractured specimens of the genus Siphonodella were found in 
the Upper K Zone Beds. One specimen consists of the anterior quarter of the 
platform, and the other of the anterior quarter of the platform and the anterior blade. 
One of the specimens has one rostral ridge and the other two rostral ridges, developed 
on either side of the carina. It is not possible to refer the specimens to any species. 

Genus SPATHOGNATHODUS Branson & Mehl 1941 

1856 Ctenognathits Pander (partim) : 32 (non Ctenognathus Fairmaire 1843). 

J 933 Spathodus Branson & Mehl : 41 (non Spathodus Boulenger 1900). 

1940 Pandorina Stauffer 428 (non Pandorina Bory de St. Vincent 1827, nee Scacchi 1833). 

1941 Spathognathodus nom. nov. Branson & Mehl : 98, (pro Spathodus Branson & Mehl 1933). 
1945 Mehlina Youngquist : 363. 

1957 Ctenognathus (Pandorinellina) Muller & Miiller : 1083. 
T 959 Pandorinellina Hass 378, (pro Pandorina Stauffer 1940). 
1959 Branmehla Hass 381. 



222 BRITISH AVONIAN CONODONT FAUNAS 

1959 Ctenognathodus nom. nov. Fay : 195 (pro Ctenognathits Pander 1856). 

1959 Ctenognathus (Ctenognathodus) Fay : 195. 

1959 Ctenognathodus (Mehlina) Fay 195. 

1962 Spathognathodus (Bispathodus) Miiller : 114. 

Type species. Ctenognathus murchisoni Pander 1856. 

The name Pandorinellina was first used by Miiller & Miiller (1957 : 1083) but was 
clearly attributed by them to Hass in the (then forthcoming) Treatise. Article 50 
of the Code of Zoological Nomenclature justifies the attribution of the genus to Hass. 

Spathognathodus anteposicornis Scott 
Plate 3, figs. 5a-8b 

1961 Spathognathodus n. sp. A Scott & Collinson : 132, PI. 1, figs. 12-15. 
1961 Spathognathodus anteposicornis Scott : 1224, text-fig. 2H - K. 

Material. 59 specimens : figured, X 540, X 541, X 542, X 543. 
Range. North Crop KL 19-ZLA 15, Avon Gorge K2 i-Z 28. 

Description. The unit is elongate, being two to three times as long as the 
highest anterior denticles ; it is straight in oral view, and highest at the anterior. 
The anterior 3 denticles are the largest, standing twice as high as the remaining blade 
denticles, the medial denticle of the three usually being highest. The remaining 
denticles are of equal height over the medial third, gradually decreasing in size 
posteriorly over the posterior third ; they are erect, basally fused and blunt tipped. 
The aboral edge is straight (PI. 3, fig. 5a) to gently arched (PI. 3, fig. 7a). A lateral 
denticle, sub-circular in cross-section, is developed high on the inner side of the unit 
over the anterior portion of, or immediately anterior to, the basal cavity, the tip 
generally being about equal in height to the adjacent denticles of the blade. 

In aboral view the basal cavity is large and flaring, with an anterior pit. The 
cavity occupies the median third and extends in both directions as an aboral groove. 
The outer margin of the cavity is subcircular (PI. 3, fig. 5b) to biconvex (PI. 3, fig. 6b). 

Remarks. Scott (1961 : 1224) described this species from the Louisiana Lime- 
stone, which he regarded as Upper Devonian. Our specimens, which have a 
restricted range above the Avonian occurrence of the genus Siphonodella, would 
appear to be stratigraphically younger. Their occurrence in the present faunas may 
be the result of one or more of at least three different factors : an independent 
phylogenetic origin, so that they are homoeomorphs of Scott's S. anteposicornis : a 
greater stratigraphic range for that species than has been hitherto supposed : or a 
Lower Carboniferous age for the Louisiana Limestone. Without firm evidence in 
support of any one interpretation, it seems preferable to assign the present specimens 
to 5. anteposicornis Scott. 

One feature of the stratigraphically older specimens of this species (PI. 3, fig. 6a), is 
the prominent square antero-aboral angle of the blade, and the posterior inclination 
of the three large anterior denticles. These features, though present, are less marked 
in stratigraphically younger specimens (e.g. PI. 3, fig. 7a). There also seems to be an 



BRITISH AVONIAN CONODONT FAUNAS 



223 



anterior migration of the lateral denticle in stratigraphically younger specimens in 
the present faunules, but the samples are too small to justify any firm conclusion. 

Spathognathodus bischoffi sp. nov. 
Plate 4, figs. ia-4c 

1956 Spathognathodus costatus (E. R. Branson) Bischoff & Ziegler : 166, PI. 13, fig. 3. 

J 957 Spathognathodus costatus (E. R. Branson) Bischoff : 56, PL 4, fig. 28. 

J 957 Spathognathodus costatus (E. R. Branson) Ziegler in Fliigel & Ziegler ; PI. 1, figs. 15, 18 

only. 
*959 Spathognathodus costatus (E. R. Branson) Helms : PL 111, figs. 2-4. 
J 959 Spathognathodus costatus (E. R. Branson) Voges : 297, text-fig. 5, fig. 1. 
1962 Spathognathodus costatus costatus (E. R. Branson) Ziegler : 107, 108, PL 14, figs. 1-6, 

8-10. 

Derivation of name. In honour of Dr. G. Bischoff. 

Diagnosis. Elongate spathognathodid with, a greatly laterally expanded 
pseudopolygnathid-type basal cavity, a central oral blade of very uniform, confluent, 
blunted denticles, and a series of about twelve strong, low, regular, laterally-elongate 
nodes developed along whole inner length of unit except for anterior blade. Outer 
oral surface of cup may be feebly nodose. 

Material. 10 specimens : Holotype X 401, Paratypes (all figured) X 398, X 400, 
X399- 

Type locality and horizon. Honnetal, West Germany to VI Zone-Upper 
costatus Zone, Roadside cutting (Ziegler 1962). 

Description. These elongate spathognathodids have an anterior blade two to 
three times as deep as the posterior end of unit. The anterior blade consists of about 
3 to 4 confluent, but apically discrete denticles, their apices being bluntly pointed. 
The anterior edge is straight and deep, making an angle of 80 "-90° with the aboral 



Lateral denticles 



Orol edge 



Posterior edge 



Posterior portion of blade 




Anterior denticle 



____— -Anterior edge 
Antero-aborol angle 



Anterior portion o( 
blade 



Aboral edge 
/ Basal cavity 

Cavity lips 
Fig. 46. Spathognathodus sp. showing morphological terms used in the text. 



224 BRITISH AVONIAN CONODONT FAUNAS 

edge, the antero-aboral angle being bluntly rounded to angular and conspicuous. 
The median denticles, posterior to the blade, are confluent for their whole length, 
their individual tips being only rarely discernible. Those in the median two-thirds 
of the unit are of uniform height, the posterior ones being shorter, and having 4 to 6 
conspicuous apices. 

The basal cavity is longitudinally restricted but makes a conspicuous feature in 
lateral view. 

In oral view, the blade is seen to be gently curved in a horizontal plane, although 
only left forms are known. The denticles are conspicuously laterally expanded to 
give a platform-like appearance to the whole unit. The size of the platform increases 
during ontogeny (cf. PI. 4, figs, ia & 4a). There are up to 14 transverse denticles 
developed, those near mid-length being the widest, giving the platform a general 
biconvex outline in oral view. Deep transverse troughs separate the denticles, and 
there is a tendency for a feeble longitudinal trough to develop also. 

In aboral view the asymmetrical laterally expanded basal cavity is a conspicuous 
feature, both its lateral expansion and its asymmetry increasing in ontogeny. Its 
transverse axis lies obliquely to the longitudinal axis of the unit, the outer (convex) 
extension pointing more posteriorly. It extends to the posterior end of the unit as a 
deep and wide but gradually narrowing cavity, and as a slit-like groove along the 
anterior part of the blade. 

Spathognathodus coaptus (Branson & Mehl) 
Plate 7, figs, ga-nc 

1934 Spathodus coaptus Branson & Mehl : 275, PI. 22, fig. 16. 

1938 Spathodus elongatus Branson & Mehl (partini) : 139, PI. 23, fig. 6 only. 

1939 Spathodus crassidentatus Branson & Mehl ; Cooper : 413, PI. 45, fig. 19. 
1939 Spathodus aciedentatus E. R. Branson ; Cooper : 413, PI. 45, figs. 26, 28, 44. 
x 939 Spathodus chouteauensis Cooper : 413, PI. 45, fig. 20. 

1939 Spathodus isus Cooper : 413, PI. 45, fig. 33. 

1939 Spathodus strigilis Huddle ; Cooper : 416, PI. 45, fig. 37. 

1939 Spathodus sulciferus Branson & Mehl ; Cooper : 416, PI. 45, figs. 17, 18. 

1949 Spathognathodus sulciferus (Branson & Mehl) Youngquist & Patterson : 72, PI. 15, fig. 1. 

1949 Spathognathodus crassidentatus (Branson & Mehl) Youngquist & Patterson : 71, PI. 15, 

fig. 2. 

1949 Spathognathodus aciedentatus (E. R. Branson) Youngquist & Patterson : 17, PI. 15, 

fig- 3- 
? 1949 Spathognathodus aciedentatus (E. R. Branson) Thomas : 412, PI. 4, fig. 7. 
1951 Spathognathodus macer (Branson & Mehl) Youngquist & Downs : 791, PI. 3, figs. 

1, 2. 
1958 Spathognathodus crassidentatus Branson & Mehl ; Freyer : 85, PI. 6, fig. 138. 
1964 Spathognathodus crassidentatus Branson & Mehl ; Rexroad & Scott : 48, PI. 3, figs. 

7.8. 

Material. 68 specimens : figured, X 453, X 454, X 436. 

Range. Avon Gorge Z i-Z 38. 

Description. This is a straight bladed spathognathodid, with a straight aboral 



BRITISH AVONIAN CONODONT FAUNAS 225 

edge. The 3 or 4 anterior denticles are higher than those of the rest of the blade. 
The number of oral denticles is variable but averages 15. The denticles of the oral 
edge are of uniform elevation with the exception of the posterior two or three, which 
may be slightly lower. The basal cavity is situated at the mid-length of the unit and 
is circular in outline. 

The denticles of the oral edge are of fairly uniform elevation, with the exception of 
those at the posterior tip, which are slightly lower, and those at the anterior, which 
rise gradually to form an anterior blade. The anterior and posterior edges are 
straight, and form right angles with the aboral edge. The aboral edge is straight. 
The basal cavity is sub-circular in outline and centrally situated. 

Remarks. Spathognathodus coaptus closely resembles 5. crassidentatus and S. 
denticulatus. In S. crassidentatus the aboral edge is arched in the posterior two 
thirds. In S. denticulatus the basal cavity is narrow and elongate. 

Spathognathodus costatus costatus (E. R. Branson) 

Plate 3, figs. I3a-i5b 

1934 Spathodus costatus E. R. Branson : 303, PI. 27, fig. 13. 

1938 Spathodus costatus E. R. Branson ; Branson & Mehl : 132, 136, PI. 33, fig. 1. 
1944 Spathodus costatus E. R. Branson ; E. B. Branson : 181, PI. 32, fig. 1. 
? 1949 Spathognathodus costatus (E. R. Branson) Thomas : 409, 412, PI. 4, fig. 10. 
non 1956 Spathognathodus costatus (E. R. Branson) Bischoff & Ziegler : 166, PI. 13, fig. 3. 
non 1957 Spathognathodus costatus (E. R. Branson) Bischoff : 56, PI. 4, fig. 28. 
non 1957 Spathognathodus costatus (E. R. Branson) ; Ziegler in Fliigel & Ziegler : PI. 1, 

figs. 15, 18 only. 
non 1959 Spathognathodus costatus (E. R. Branson) Helms : PI. in, figs. 2-4. 
non 1959 Spathognathodus costatus (E. R. Branson) Voges : 297, text-fig. 5, fig. 1. 
non 1959 Spathognathodus cf. costatus (E. R. Branson) Voges : 297, PI. 34. 
non 1962 Spathognathodus costatus costatus (E. R. Branson) Ziegler : 107, 108, PI. 14, figs. 1-6, 
8-10. 
? 1964 Spathognathodus costatus costatus (E. R. Branson) Higgins, Wagner-Gentis & 
Wagner : PI. 5, fig. 21. 

Material. 170 specimens : figured, X 455, X 166, X 456. 

Range. North Crop ZLA 2-ZL 10, Avon Gorge K 18-Z 28. 

Description. The unit is slightly arched and bowed, being highest at the anterior 
end, although the anterior blade is only about one third as high again as the posterior 
end. The oral profile is sigmoidal, the anterior blade being highest and consisting of 
3 or 4 large denticles, the tallest of which is either the anterior-most or penultimate 
anterior denticle. The denticles of the mid-region are of equal height, and lower than 
the anterior denticles, and the unit shallows posteriorly. Situated on the inner side 
of the unit is a row of peg-like nodes, 5 to 8 in number, which tend to jut out of the 
unit. These nodes may be joined to the main unit by transverse ridges, but these 
ridges lie below the level of the node tips. 

In aboral view the cavity occurs in mid-length, is fairly large and symmetrical, and 
is widest at its mid-point. It extends as a narrow groove to near the posterior 
termination and for a short distance along the anterior blade. 



226 BRITISH AVONIAN CONODONT FAUNAS 

Spathognathodus costatus sulciferus (Branson & Mehl) 
Plate 3, figs. i6a-i8c 

1934 Spathodus sulciferus Branson & Mehl : 274, PI. 22, figs. 12, 13. 
1934 Spathodus spinulicostatus E. R. Branson : 305, PI. 27, fig. 19. 
1938 Spathodus spinulicostatus E. R. Branson ; Branson & Mehl : 132, PI. 33, fig. 2. 
non 1939 Spathodus sulciferus Branson & Mehl ; Cooper : 416, PL 45, figs. 17, 18 (fig. 17 = S. 

cyrius, fig. 18 = S. crassidentatus). 
1944 Spathodus spinulicostatus E. R. Branson ; E. B. Branson PL 32, fig. 2. 
1944 Spathognathodus sulciferus (Branson & Mehl) Branson & Mehl in Shinier & Shrock : 

PL 94, fig. 2. 
? 1961 Spathognathodus costatus spinulicostatus (E. R. Branson) Higgins, Wagner-Gentis & 

Wagner : PL 5, fig. 22. 

Material. 29 specimens : figured, X 457, X 458, X 459. 

Range. North Crop ZLA 4-ZL 10, Avon Gorge K 18-Z 26. 

Description. The unit is straight, very slightly arched and highest at the 
anterior end. The anterior blade consists of 3 to 4 high denticles, its oral outline 
being gently convex upward. The medial part of the unit possesses denticles of 
equal height, the posterior part having denticles which become progressively lower 
toward the posterior termination. Both lateral faces of the unit bear nodes, the 
inner row of about 10 being similar to the inner row of S. costatus costatus, with the 
largest nodes lying in the medial position and having depressed and inconspicuous 
transverse connecting ridges. The outer lateral dentition is confined mainly to the 
area of the oral side of the cavity lip and consists of 1 to 3 large fused nodes of lower 
height than the inner row. The posterior part of the outer face occasionally bears 
isolated denticles (PI. 3, fig. 16). 

In aboral view the cavity is large, medial and sub-symmetrical, tending to have a 
greater amount of flaring on the outer side ; it is about twice as long as wide and runs 
posteriorly as a narrow groove. It is laterally expanded, and wider at the anterior 
end. 

Remarks. S. costatus sulciferus is obviously very closely related to 5. costatus 
costatus, differing only in the addition of lateral denticles on the outer side. Further 
enlargement of the outer platform gives species referable to the genus Pseudopoly- 
gnathus, although that genus is polyphyletic. 

Spathognathodus crassidentatus (Branson & Mehl) 
Plate 3, figs. ia~4b 

1934 Spathodus crassidentatus Branson & Mehl : 276, PL 22, figs. 17, 18. 

1934 Spathodus crassidentatus Branson & Mehl ; E. R. Branson : 303, PL 27, fig. 12. 

1934 Spathodus denticulatus E. R. Branson : 305, PL 27, fig. 17. 

1934 Spathodus aciedentatus E. R. Branson : 306, PL 27, figs. 21, 23. 

1934 Spathodus strigilis Huddle : 89, PL 7, fig. 15 ; PL 12, fig. 11. 

1934 Spathodus parvus Huddle : 90, PL 7, fig. 16. 

1938 Spathodus crassidentatus Branson & Mehl ; Branson & Mehl : 132, 137, PL 33, fig. 5. 

1938 Spathodus elongatus Branson & Mehl (partim) : 139, PL 34, fig. 9 (non PL 34, fig. 6 = 5. 
elongatus) . 



BRITISH AVONIAN CONODONT FAUNAS 227 

!939 Spathodus crassidentatus Branson & Mehl ; Cooper : 413, PI. 45, fig. 19. 

J 939 Spathodus aciedentatus E. R. Branson ; Cooper : 413, PI. 45, figs. 26, 28, 44. 

T 939 Spathodus chouteauensis Cooper : 413, PI. 45, fig. 20. 

T 939 Spathodus strigilis Huddle ; Cooper : 416, PI. 45, fig. 37. 

J 939 Spathodus sulciferus Branson & Mehl ; Cooper (partim) : 416, 420, PI. 45, fig. 18. 

*939 Spathodus isus Cooper : 413, PI. 45, fig. 33. 

1943 Spathodus strigilis Huddle ; Cooper & Sloss : 175, PI. 28, figs. 3, 4, 10, 12. 

1943 Spathognathodus crassidentatus (Branson & Mehl) Cooper & Sloss : 175, PI. 28, fig. 1. 

1949 Spathognathodus crassidentatus (Branson & Mehl) Youngquist & Patterson : 71, PI. 15, 

fig. 2. 

1949 Spathognathodus aciedentatus (E. R. Branson) Youngquist & Patterson : 71, PI. 15, fig. 3. 

1949 Spathognathodus quintidentatus Thomas : 429, PI. 4, figs. 8, 9. 

1949 Spathognathodus aciedentatus (E. R. Branson) Thomas, PL 4, fig. 7. 

1956 Spathognathodus crassidentatus (Branson & Mehl) Bischoff & Ziegler (partim) : 166, 
PI. 13, fig. 14 (non PI. 13, fig. 13). 

z 957 Spathognathodus crassidentatus (Branson & Mehl) Bischoff : 56. 

1961 Spathognathodus crassidentatus (Branson & Mehl) Freyer : 85, PI. 6, fig. 138. 

1964 Spathognathodus crassidentatus (Branson & Mehl) Rexroad & Scott : 48, PI. 3, figs. 7, 
8. 

Material. 222 specimens : figured, X 460, X 461, X 462, X 463. 
Range. North Crop KL 2-ZLA 33, Avon Gorge K 17-Z 38. 

Description. This is a simple arched and bowed unit, which is highest at the 
anterior. The anterior blade consists of 3 to 6 tall, massive denticles which are 
basally confluent, with discrete blunt apices, the denticles in the medial part of the 
blade being highest. The mid-third of the unit consists of denticles of even height, 
conspicuously lower than the anterior denticles. The denticles of the posterior third 
decrease in height towards the posterior termination. The total number of denticles 
ranges from 17 to 22. 

In aboral view a large cavity, situated medially, is symmetrically flared and widest 
just anterior to its mid-point. The cavity is extended both anteriorly and posteriorly 
as a narrowing groove, the posterior extension being the longer. 

Remarks. This species is common, and, as was pointed out by Rexroad and Scott 
(1964 : 49), is highly variable. Although we accept most of the synonomy of those 
authors, we believe that forms with a very much greater denticle density should not 
be included under S. crassidentatus, but should be referred to S. cyrius (Cooper) (see 

P- 234)- 

Spathognathodus cristulus Youngquist & Miller 

Plate 8, figs. I4a-i8d 

1949 Spathognathodus cristula Youngquist & Miller : 621, PI. 101, figs. 1-3. 

1957 Spathognathodus cristula Youngquist & Miller ; Rexroad : 38, PI. 3, figs. 16, 17. 

1958 Spathognathodus cristula Youngquist & Miller ; Rexroad : 25, PI. 6, figs. 3, 4. 

T961 Spathognathodus cristula Youngquist & Miller ; Rexroad & Burton : 1156, PI. 141, 
fig. 9- 

1962 Spathognathodus cristula Youngquist & Miller ; Rexroad & Liebe : 511, table 1. 

1964 Spathognathodus cristula Youngquist & Miller ; Rexroad & Furnish : 674, PI. 111, 

fig- 15- 

1965 Spathognathodus cristula Youngquist & Miller ; Rexroad & Nicoll : 26, PI. 1, figs. 1, 2. 



228 BRITISH AVONIAN CONODONT FAUNAS 

Material. 278 specimens : figured, X 464, X 465, X 466, X 467, X 468. 
Range. North Crop CYD 7, Avon Gorge Z i-D 26. 

Description. This spathognathodid bears 8 to 12 denticles along its oral edge, 
of which the most anterior is the largest. The remaining denticles decrease uni- 
formly in size towards the posterior end, so that the general form of the denticulate 
edge is continuously convex, being lowest posteriorly. The basal cavity extends for 
about two-thirds the length of the unit. It is widest at the anterior end, and is 
continuous to the posterior end, being biconvex in outline. 

The short blade is distinguished by a deep anterior end, with a high anterior 
denticle. The anterior edge of the unit slopes conspicuously forward so that its 
antero-aboral projection lies in front at the tip of the denticle. The antero-aboral 
angle is either bluntly rounded or more or less angular, forming an angle of about 90 °. 
The anterior edge is straight. The anterior denticle is about half as long again as 
that adjacent to it, and about twice as wide. The remaining denticles of the bar 
decrease uniformly in size towards the posterior end. Except for the two posterior 
denticles which tend to be conspicuously smaller than the rest, the denticles are 
discrete only at their bluntly rounded tips. They have convex lateral faces and 
stand erect to the bar. The posterior margin, which is formed of the two most 
posterior denticles, tends to slope posteriorly. In lateral view the aboral edge of the 
unit is straight in the anterior third of the unit, but is concave posteriorly, because 
of the flare of the basal cavity. This cavity is slightly asymmetrical, but is strongly 
convex in outline and extends for about two thirds the length of the aboral surface. 
Its maximum width is only about half or a third of its total length and its greatest 
depth and width are anterior. It extends anteriorly as a median slit along the 
anterior blade. 

There is a tendency in some specimens for the posterior denticles to be progressively 
posteriorly inclined towards the posterior end. In some specimens the anterior 
aboral angle is rather less than 90 ° and the apical denticle is more sharply triangular 
in lateral view than in other specimens. 

Remarks. The first stratigraphic occurrence of Spathognathodus cristulus in the 
Avonian of the Bristol area is considerably older than that known in other parts of 
the world. 

Spathognathodus elongatus (Branson & Mehl) 
Plate 7, figs. ia-5b 

1938 Spathodus elongatus Branson & Mehl : 139, PI. 34, fig. 6 {-non PI. 34, fig. 9 = S. crassi- 

dentalusl) . 
1944 Spathodus elongatus Branson & Mehl ; E. B. Branson : PI. 39, fig. 6, (non PI. 39, fig. 

9 = S. crassidentatus?). 

Material. 48 specimens : figured, X 472, X 473, X 474, X 475. 

Range. North Crop KL 19-ZL 8, Avon Gorge K 4-Z 13. 

Description. The blade is straight or gently curved in oral view, being long and 



BRITISH AVONIAN CONODONT FAUNAS 229 

shallow over the whole length. The denticles are highest at the anterior end, 
decreasing in height towards the position of the anterior end of the cavity, beyond 
which they increase in size towards the posterior end of the cavity, and then decrease 
gradually towards the posterior end of the unit. The denticles are compressed, fused 
at their bases, and free at their tips ; about 20 in number. Longitudinal 
' shoulders ' are developed on the lateral faces below the bases of the denticles. The 
aboral outline is straight to slightly arched. The very shallow depth of the blade 
just anterior to the basal cavity gives a ' sagging ' profile to the unit. The length 
of the unit is about four times the maximum depth. 

The cavity is symmetrical, elongate and shallow, with a slight appearance of cups. 
It narrows to grooves at both ends, which extend about halfway along aboral edges 
towards anterior and posterior ends. 

Remarks. Our specimens agree perfectly with the figured holotype of S. elongatus 
(Branson & Mehl, 1938A, PL 34, fig. 6), although their description is scarcely adequate 
to distinguish this from other species. Within our fauna there appear to be two 
forms ; the first includes those with free standing fine denticles (PL 7, fig. 5a) which 
tend to be sharper, longer and of more regular length than those of the second group, 
which have laterally compressed denticles (PL 7, fig. ia). The long, free-standing 
denticles of this first group are reminiscent of S. denticulatus (E. R. Branson) (1934, 
PL 27, fig. 17), but the differences in relative length of the units and anterior dentition 
preclude us from placing these forms within that species. Cooper (1939 : 413) refers 
the paratype (PL 34, fig. 9) to a new species S. chouteauensis. Rexroad & Scott 
(1964 : 48) refer both the holotype and paratype to S. crassidentatus (Branson & 
Mehl). It is possible that the paratype, referred to S. chouteauensis by Cooper, is 
referable to S. crassidentatus (Branson & Mehl) but the holotype is definitely a 
separate species. 

Spathognathodus plumulus plumulus sp. et subsp. nov. 
Plate 1, figs. ia-2c, 5, 6 

Derivation of name. From the plume-like anterior blade. 

Diagnosis. Spathognathodid with plume-like anterior blade, denticles of which 
decrease rapidly in size anteriorly from a massive denticle at posterior end of blade. 
Series of lateral nodes present, developed on the outer side only, above the basal 
cavity. 

Material. 442 specimens : Holotype X 476, Paratypes X 379, X 380, X 381 
(all figured). 

Type locality and horizon. R. Clydach, Nr. Gilwern, K Zone North Crop. 
Sample KL 4. 

Range. North Crop KL i-KL 16, Avon Gorge K 2-K2 1. 

Description. The blade is plume-like in anterior third, consisting of 3 to 6 
denticles, decreasing rapidly in height anteriorly from a tall massive denticle situated 
immediately anterior to the basal cavity. The remainder of the unit is low, consist- 



230 BRITISH AVONIAN CONODONT FAUNAS 

ing of about 16 fused, laterally compressed denticles, those in the posterior third of 
the unit tending to be the largest. The oral profile, posterior to the blade, is gently 
convex. Lateral denticles are developed on the outer side above the basal cavity 
and number from 2 to 5 ; they tend to form a short platform, restricted to the region 
of the basal cavity, rather than occurring as laterally divergent peg-like denticles. 
The aboral lateral profile is conspicuously straight, being arched behind the cavity. 

In aboral view the cavity is ovate, slightly asymmetrical, the flared side being the 
narrower. The long axis is parallel to the long axis of the unit, equal to, or only 
slightly greater than, the maximum lateral width of the cavity. The cavity may 
extend as a faint groove for a short distance along the anterior and posterior blades. 

Remarks. Ziegler (1960A, PI. 3, figs. 8, 9) described forms referred by him to 5. 
tridentatus, which appear to be referable to S. plumulus plumulus. The form figured 
by him (i960 A, PI. 3, fig. 7) as S. sulci jer us is distinct from Branson & Mehl's type 
specimen which is, in fact, a senior synonym of S. spinulicostatus (E. R. Branson 
1934). Ziegler's specimen appears from its tall blade and the nature of the anterior 
face to be closely related to S. plumulus plumulus, but its lack of platform develop- 
ment precludes its inclusion in that species, although it may be a form ancestral to 
spathognathodids with high plume-like blades. 

S. plumulus plumulus is probably ancestral to Clydagnathus (see p. 85). The 
lateral profile of the blade, with its sharply descending oral surface, short anterior 
edge, and rounded antero-aboral angle, is also very similar to that of Scaphignathus. 

Spathognathodus plumulus nodosus sp. et subsp. nov. 
Plate 1, figs. 3a~4C 

Derivation of name. From the additional nodes on the inner side of cup. 

Diagnosis. Subspecies of S. plumulus with one or more nodes developed on inner 
platform expansion. 

Material. 14 specimens : Holotype X 382, Paratype X 383. 

Type locality and horizon. R. Clydach, Nr. Gilwern, Lower K Zone North 
Crop. Sample KL 2. 

Range. North Crop KL i-KL 6, Avon Gorge K-8. 

Description. This form is similar to S. plumulus plumulus in gross morpho- 
logical detail, but the inner oral lip of the expanded cavity bears one or more nodes. 

Remarks. As in the S. tridentatus group, the S. plumulus group develops lateral 
denticles on the inner and outer lateral margins of the cup. In 5. plumulus nodosus 
the development towards a pseudopolygnathid morphology (as in the S. aculeatus 
and S. tridentatus groups) is seen. The development of the denticle ranges from 
weak to strong. 

Spathognathodus plumulus shirleyae subsp. nov. 
Plate 1, figs. 7a-8c 

Derivation of name. After Mrs. Shirley Osborn. 



BRITISH AVONIAN CONODONT FAUNAS 231 

Diagnosis. Spathognathodid with plume-like anterior blade, having one node 
developed on outer lateral face above basal cavity. 

Material, io specimens : Holotype X 384, Paratype X 385 (both figured). 

Type locality and horizon. R. Clydach, Nr. Gilwern, Lower K Zone North 
Crop. Sample KL 2. 

Range. North Crop KL 2-KL 3, Avon Gorge K 4-K 8. 

Description. The blade is short and thin, the anterior part consisting of a 
posterior high, massive, recurved, laterally compressed denticle, and the denticles 
rapidly decreasing in height anteriorly, to give a plume-like effect. The medial and 
posterior parts of the unit consist of low, fused, laterally compressed, erect to slightly 
posteriorly inclined denticles. Above the anterior part of the outer cavity lip, a 
single lateral node denticle arises, which is sub-circular in cross-section. 

In aboral view the cavity is elliptical, slightly flared and its long axis is concordant 
with the long axis of the unit. 

Remarks. This form appears to occupy the same position within the S. plumulus 
lineage as does S. anteposicornis Rexroad & Scott within the 5. tridentatus lineage. 
The small size of all the present specimens might be interpreted to mean that they 
are a growth stage of S. plumulus plumulus sp. nov., but the presence of three 
denticles in specimens of that species of comparable small size (PI. 1, fig. 6) and the 
restricted range of the present subspecies appear to justify its recognition as distinct. 

Spathognathodus pulcher (Branson & Mehl) 
Plate 4, figs. 9a-nc 
1938 Spathodus pulcher Branson & Mehl : 139, PI. 34, figs. 7, 8. 

Material. 59 specimens : figured, X 386, X 512, X 513. 

Range. North Crop KL 19-ZLA 15, Avon Gorge Z 12-C 7. 

Description. The blade is long and thin, being highest at the anterior and 
decreasing gradually to a point anterior to the basal cavity, where the profile becomes 
straight, sloping off abruptly at the posterior termination. The 14 to 15 sub-circular 
denticles are erect, short, fused at the bases, and free at the sharply pointed tips. 
The cavity is elongate, expanded, and occurs in the posterior half of the unit, 
terminating immediately anterior to the posterior end. The anterior part of the 
blade is about twice as deep as the posterior. 

Remarks. This form differs from S. crassidentatus s.s., in the lack of a distinct 
high blade at the anterior end, and in the posterior (rather than medial) position of 
the basal cavity. It resembles S. elongatus in the anterior half, but the sudden 
termination immediately posterior to the basal cavity is distinctive (Branson & Mehl 
1938A : 139-140, PI. 34, figs. 7, 8). It is very similar to a form described by Branson 
& Mehl (1938A) asS. elongatus (PL 34, fig. 9) which was referred by Cooper (1939) to a 
new species, S. chouteauensis. Rexroad & Scott (1964) refer this to S. crassidentatus, 
but it would appear not to fit even their broad terms for the species. The present 
specimens are also close to S. stabilis. 



232 BRITISH AVONIAN CONODONT FAUNAS 

Spathognathodus scitulus (Hinde) 
Plate 8, figs. 9a-nd 

1900 Polygnathus scitulus Hinde : 343, PI. 9, figs. 9-1 1 only. 

1928 Panderodella scitula (Hinde) Holmes : 16, PI. 6, figs. 26, 28 only. 

i960 Spathognathodus scitulus (Hinde) Clarke : 21, PI. 3, figs. 12, 13. 

1962 Spathognathodus scitulus (Hinde) Rexroad & Collinson : 20, PI. 2, figs. 14, 19, 29-31. 

Material. 19 specimens : figured, X 391, X 392, X 393. 
Range. North Crop CYD 6-3D 14/15, Avon Gorge C 15-D 27. 

Description. This spathognathodid is characterized by having an oral outline 
that is straight in the mid-third, but which plunges steeply towards the posterior end. 
It has relatively few denticles on the oral edge and a widely flared, arched, basal 
cavity on the outer lateral face. The posterior end is shallow and pointed. 

This short spathognathodid has a prominent plough-like antero-aboral area which 
may sometimes develop an irregular anterior edge. The antero-aboral margin is 
acute and more or less pointed and its posterior edge is feebly convex. The anterior 
edge of the unit is generally straight. The oral edge bears 9 denticles, which stand 
more or less erect to the general line of the blade, only their apices being discrete. 

The denticles decrease regularly in size towards the posterior end of the unit, the 
posterior 2 or 3 tending to be minute in size. The anterior denticle is much the 
largest, but the subsequent 4 or 5 denticles tend to be of rather uniform size, and the 
mid-third of the unit has a rather straight lateral edge. In outer lateral view, the 
sharp flexure of the unit and the widely flared basal cavity are prominent features. 
The posterior end of the unit is very shallow. The aboral edge is continuously 
concave and the posterior edge is bluntly pointed. The basal cavity itself is confined 
to the mid- third of the unit and it is flared only on the outer lateral side, the inner 
side being straight. 



Spathognathodus scitulus subsp. nov. A 
Plate 31, figs. I2a-c 

Material. 3 specimens : X 390 (figured). 
Range. Scotland DUN 78. 

Description. A Spathognathodus scitulus with one or two inconspicuous 
accessory denticles developed on the anterior edge of the main denticle. 

The present specimens agree with typical individuals of 5. scitulus (e.g. those 
illustrated by Rexroad & Collinson 1963, and Clarke i960) except that the " cusp " 
(the most anterior denticle of the blade) has two small confluent denticles on its 
anterior aboral edge, which are developed parallel to the anterior margin. The 
denticles posterior to the main denticle, the general form of the blade, and the 
general structure and asymmetry of the basal cavity are otherwise similar to those 
of Spathognathodus scitulus s.s. 



BRITISH AVONIAN CONODONT FAUNAS 233 

Spathognathodus cf. catnpbelli Rexroad 
Plate 8, figs. ia-4c 

1957 Spathognathodus campbelli Rexroad : 37, PI. 3, figs. 13-15. 
i960 Spathognathodus pusillus Clarke : 20-21, PI. 3, figs. 10, 11. 
1965 Spathognathodus cf. campbelli Rexroad ; Rexroad & Nicoll : 26, PI. 1, fig. 6. 

Material, ii specimens : figured, X 450, X 451, X 452, X 435. 

Range. North Crop CYD 6-3D 19. 

Description. The most distinctive features of the present specimens are the 
deep and relatively short blade, which is almost as deep as the longest oral denticles ; 
the series of up to 20 laterally compressed denticles of which the largest occurs at 
about mid-length ; the marked flaring of the basal cavity, which is confined to the 
posterior half of the unit ; and the gentle posterior deflection in a vertical plane of 
the posterior half of the unit. In lateral view the oral margin is sharply denticulated, 
tending to be straight and rather sloping in the anterior half, and more or less convex 
in the posterior half. There are 17 to 20 denticles on the oral edge of the blade. 
These show a rough increase in size from the anterior denticle to the denticle at about 
mid-length of the blade, which is the largest of the whole blade and is feebly inclined 
posteriorly to the basal surface of the blade. The other denticles of the anterior part 
of the blade are more or less erect and are confluent for most of their length, although 
their apical portions are discrete and pointed. The denticles of the posterior part of 
the blade are all inclined posteriorly. They are discrete for a greater part of their 
length than those of the anterior part of the blade, and the degree of posterior 
inclination tends to increase towards the posterior end of the blade. Those in the 
posterior quarter of the blade tend to be the smallest. The posterior blade decreases 
in depth posteriorly and the posterior end is shallow and bluntly spatulate. It is 
also conspicuously depressed in a vertical plane towards the posterior end. The 
other striking feature in lateral view is the widely flaring and elongate basal cavity, 
the anterior end of which is aligned with the anterior edge of the largest denticle. 

In aboral view the cavity has a strongly biconvex outline and is extended virtually 
to the posterior end of the blade. It is continued anteriorly to the anterior edge of 
the main denticle as a very inconspicuous and narrow slit. 

Remarks. The present specimens differ somewhat from those described by 
Rexroad in having a rather conspicuously developed denticle at about mid-length. 
In other respects the specimens are closely similar, especially in the general form of 
the basal cavity, which tends to be more rounded anteriorly than it is posteriorly, and 
to have its deepest point near the anterior end. The longitudinal line immediately 
above the level of the navel, which marks the thin basal edges of the unit, is well seen 
under certain conditions of lighting. 

Spathognathodus cf. cristulus Youngquist & Miller 
Plate 8, figs. 7a-8c, I2a-i3b 

1938 Spathognathodus regularis Branson & Mehl (partim) : 137, PI. 34, fig. 2 only (non PI. 34, 
figs. 1, 3, 10 = S. regularis). 



j.U BRITISH .WOMAN CONODONT FAUNAS 

Material. 387 specimens : figured, X 554-X 557. 

Range. North Crop ZLA 2-ZLA 33, Avon Gorge Z 35-D 27. 

Description. This species is a simple denticulate unit bearing a regular succes- 
sion of denticles which decrease in height from anterior to posterior. The anterior 
denticle tends to be massive, taller and nearly twice as wide as the remainder ; the 
next two denticles in a posterior direction tend to be fairly narrow and fused ; the 
remainder have free chevron-shaped tips and are slightly larger. 

In aboral view the cavity is large with some flaring of the lips ; it begins imme- 
diately posterior to the anterior denticle and runs to the posterior termination of the 
unit. The lips are arched anteriorly and the whole cavity is symmetrical. 

Remarks. This form agrees very closely with S. cristulus (Youngquist & Miller, 
1949 : 621, PI. 101, figs. 1-3), except that their specimens commonly have 10 smaller 
denticles, whereas the present forms have from 7 to 16 denticles. They agree 
exactly with a form included in S. regularis (Branson & Mehl 1938 A), even to the 
number of denticles. Branson & Mehl, and Rexroad & Scott (1964 : 50) recognize 
forms with one major anterior denticle within the specific terms of S. regularis, but 
since our fauna contains specimens with only one major denticle, and no specimens 
with the two anterior denticles typical of the holotype of S. regularis, there are 
obviously two separate species involved. The present specimens are compared to 
S. cristulus because of their close resemblance, but they are stratigraphically younger 
and may be a separate, perhaps ancestral, species. 



Spathognathodus cf. cyrius (Cooper) 
Plate 7, figs. I2a-i4c 

1939 Spathodus sulciferus Branson & Mehl ; Cooper (partim) : PI. 45, fig. 17, (non PI. 

45, fig. 18 = 5. cvassidentatus) . 
!939 Spathodus cyrius Cooper : 413, PI. 45, fig. 25. 
non 1943 Spathognathodus cyrius (Cooper) Cooper & Sloss : 175, PI. 28, figs. 3, 4, 10, 12 

(=5. crassidentatus) . 
1951 Spathognathodus macer Branson & Mehl ; Youngquist & Downs : 791, PI. in, 

figs. 1, 2. 

Material. 19 specimens : figured, X 470, X 469, X 471. 
Range. North Crop KL 2-ZLA 2, Avon Gorge Z i-Z 13. 

Description. This is a simple arched and bowed unit which is highest at the 
anterior end ; the anterior part consists of 3 high denticles with the medial one the 
largest. The rest of the unit is made up of lower denticles, the medial part consisting 
of denticles of equal height and the posterior part shallowing with progressively 
smaller denticles. In the medial part the denticles are very fine and fused, 2 denticles 
commonly having only one emergent oral extremity. The unit commonly bears, 
besides the large anterior denticles, 30 smaller denticles. 

The cavity is situated medially and is relatively small and pear-shaped. 



BRITISH AVONIAN CONODONT FAUNAS 235 

Remarks. This species bears a marked resemblance to S. crassidentatus and was 
included in that species by Rexroad & Scott (1964), but the very different dentition 
serves to distinguish it. The medial and posterior oral parts commonly bear 30 
denticles, as opposed to the 15 or so of S. crassidentatus. Between the anterior part 
of the cavity and the anterior high blade, this species has 7 to 8 denticles whereas S. 
crassidentatus has only 2 to 3. Cooper's holotype has a total of only 20 denticles, but 
is otherwise very similar to the present specimens. The present specimens also 
resemble those described by Cooper (1939, PI. 45, fig. 17 only) as Spathodus sulciferus 
Branson & Mehl (fig. 18 of Cooper's PI. 45 is probably 5. crassidentatus) and those 
described as S. macer by Youngquist & Downs (1951, PI. in, figs. 1, 2). S. chou- 
teauensis Cooper (1939, PI. 45, fig. 20) is also broadly similar and also has resem- 
blances to S. crassidentatus. 



Spathognathodus cf. robustus (Branson & Mehl) 
Plate 7, figs. 6a-7c 

1934 Spathodus robustus Branson & Mehl : 189, PI. 17, fig. 21. 

Material. 17 specimens : figured, X 387, X 388. 
Range. North Crop KL 19-ZLA 14, Avon Gorge K2 1. 

Description. The unit is bar-like, being highest at the anterior end and sloping 
towards the posterior end, the oral outline being nearly straight. The anterior 
denticles tend to be massive. Smaller denticles appear on the anterior edge of the 
anteriormost massive denticle, giving a posteriorly inclined anterior edge which 
makes a sharp angle of about 60 °, with the aboral edge. The denticles in the median 
part of the unit are fused, two denticles often fusing into one free tip. The posterior 
bar-like part of the unit is shallow, twisted and depressed downwards, the denticles 
tending to be isolated and free standing and curved towards the inner side. 

In aboral view the cavity is fairly large, elongate, medially situated, about twice as 
long as wide, the wider anterior end narrowing rapidly towards the anterior of the 
unit and the other end narrowing slowly towards the posterior ; the lips are 
thickened slightly. 

Remarks. Branson & Mehl (1934, PI. 17, fig. 21) described a form very similar to 
ours as S. robustus. The dentition is very similar, except that in their specimen the 
massive anterior denticle and the isolated posterior denticles are less conspicuously 
developed than those of the present specimens. 

There appears to be a morphological trend from these specimens through such 
forms as Spathognathodus sp. B. to a pseudopolygnathid form. 

The Spathognathodus tridentatus group 

Much confusion has arisen in recent conodont literature (Sannemann 1955, 
Bischoff & Ziegler 1956, Freyer 1961 and Ziegler 1962) with regard to specimens of 
the genus Spathognathodus which develop lateral denticles. Spathognathodids with 



236 BRITISH AVONIAN CONODONT FAUNAS 

lateral denticles have been described by Branson & Mehl (1933), E. R. Branson 
(1934) and Scott (1961), from the Grassy Creek, Bushberg/Hannibal, and Louisiana 
Limestone Formations respectively. 

German workers recognized a progressive addition of denticles, firstly on the inner 
lateral face, and secondly on the outer lateral face. Forms with denticles confined 
to the inner supra-cavity position were referred to S. aculeatus (Branson & Mehl), 
whereas forms with a development of lateral denticles along the whole length of the 
unit, except for the high anterior blade, were referred to subspecies of 5. costatus 
(E. R. Branson). Scott (1962 : 1224) separated as a distinct species (S. anteposi- 
cornis), forms with a single node immediately anterior to the oral surface of the 
cavity. 

From studies of the present British conodont faunas it appears that within the 
period Upper Devonian (to V) to Lower Carboniferous (Cu II a), there has been 
multiple development of laterally nodose spathognathodids. It appears that the 
Grassy Creek (to V) form S. aculeatus (Branson & Mehl) was the first species exhibit- 
ing this trend. No other to V forms with further development of lateral denticles 
on both lateral faces are known. Forms described from Germany and identified as 
5. aculeatus by Ziegler (1961) and other authors may be distinct from S. aculeatus 
and are probably a new species. 

The further developments of this species referred by Ziegler to S. costatus costatus, 
S. costatus spinulicostatus and S. costatus ultimus are definitely not representative of 
the species S. costatus (E. R. Branson) and 5. spinulicostatus (E. R. Branson), and are 
named herein as new species, S. bischoffi sp. nov. and S. ziegleri sp. nov. 

S. costatus costatus (E. R. Branson) (= S. costatus of Branson) and S. costatus 
sulciferus (Branson & Mehl) (= S. spinulicostatus of E. R. Branson) appear to be 
restricted to an upper Cu I-Lower Cu II a range, and can be seen to develop into 
forms referable to the genus Pseudopolygnathus. The fact that species of this genus 
are found at lower horizons (e.g. the Devonian-Carboniferous boundary) indicates 
that the genus Pseudopolygnathus is polyphyletic, the ancestral forms in both cases 
probably being nodose spathognathodids, as suggested by Voges (1959). 

Forms with from 2 to 4 lateral denticles, occurring with S. costatus (sensu E. R. 
Branson) and S. spinulicostatus (sensu E. R. Branson), appear referable to S. 
tridentatus (E. R. Branson), as distinct from S. tridentatus (sensu Sannemann, 
Bischoff & Ziegler and Freyer), the latter forms being better referred to S. aculeatus 
(sensu Ziegler). 

In addition to these forms, there occurs at the base of the Lower Carboniferous in 
our sections, beneath and with the first occurrence of the genus Siphonodella, a new 
species of laterally denticulate Spathognathodus, with a plume-like anterior blade. 
Ziegler (i960 A) described as S. tridentatus a form which appears referable to our new 
species S. plumulus plumulus. This species also exhibits evolutionary addition of 
denticles on the outer lateral cup but, rather than evolving to give species of the 
genus Pseudopolygnathus, it alters by lateral shift of the anterior blade into a homoeo- 
morphic form of the genus Cavusgnathus, named herein as a new genus Clydagnathus 
(P- 85). 



BRITISH AVONIAN CONODONT FAUNAS 237 

Spathognathodus tridentatus (E. R. Branson) 
Plate 3, figs. 9a-i2c 

1934 Spathodus sulciferus Branson & Mehl ; E. R. Branson : 304, PL 27, fig. 15 ? 22 

(non PL 27, fig. 20 = S. costatus sulciferus). 
1934 Spathodus tridentatus E. R. Branson : 307, PL 27, fig. 25. 
1934 Spathodus duplidens Huddle : 91, PL 12, figs. 1-4. 

1949 Spathognathodus costatus (E. R. Branson) Thomas : 409, 412, PL 4, fig. 10. 
1949 Spathognathodus tridentatus (E. R. Branson) Thomas : 412, PL 4, fig. 11. 
non 1955 Spathognathodus tridentatus (E. R. Branson) Sannemann : PL 24, fig. 13. 
non 1956 Spathognathodus tridentatus (E. R. Branson) Bischoff & Ziegler : p. 167, PL 13, 
figs. 1, 2. 
? 1956 Spathognathodus aciedentatus (E. R. Branson) Hass PL 2, fig. 26. 
? 1957 Spathognathodus aciedentatus (E. R. Branson) Cloud, Barnes & Hass : PL 5, 

fig- 7- 
? 1959 Spathognathodus aciedentatus (E. R. Branson) Hass : PL 49, fig. 24. 
non 1959 Spathognathodus tridentatus (E. R. Branson) Voges : 658, PL 3, fig. 7. 
non i960 Spathognathodus tridentatus (E. R. Branson) Dvorak & Freyer : PL 2, figs. 9, 10. 
wok 1961 Spathognathodus tridentatus (E. R. Branson) Freyer : 89, PL 6, fig. 150. 
non 1961 Spathognathodus tridentatus (E. R. Branson) Remack-Petitot : 261, fig. 4. 

Material. 259 specimens : figured, X 394, X 395, X 396, X 397. 
Range. North Crop KL 19-ZLA 27, Avon Gorge K 21-Z 24. 

Description. The unit is straight to gently arched in the posterior part and 
slightly bowed ; it is highest at the anterior. The anterior blade is composed of 3 to 
4 high denticles, the highest being the anterior-most 2 or 3 denticles. The median 
denticles are of equal height, and the unit shallows posteriorly, the denticles becoming 
shorter, less fused, and rather sharper towards the posterior end. 

On the inner side there are developed from 2 to 4 lateral denticles, situated above 
the cavity. They are peg-like and are not connected to the main blade by transverse 
ridges. 

In aboral view the basal cavity is large and symmetrically expanded, the widest 
part being at or just anterior to the mid-point. The cavity extends in either direc- 
tion as a short aboral groove, the posterior groove being longer than the anterior. 

Remarks. This is a very common species with a limited range in our faunas. It 
is closely related to and occupies an intermediate phylogenetic position between S. 
anteposicornis and S. costatus costatus. It is also very close to S. aculeatus, but its 
higher stratigraphical position implies a distinct phylogenetic origin. For this 
reason it seems undesirable to regard it as a junior synonym of that species. The 
similarity between the two forms is, in any case, not exact. S. aculeatus has a more 
conspicuously laterally expanded basal cavity. Individuals from stratigraphically 
older samples (e.g. PI. 3, figs, na-c) tend to have a smaller number of blade denticles 
(9 to 13) behind the anterior blade than those from younger samples (e.g. PI. 3, 
figs, ioa-c), which have from 14 to 19 denticles. 



238 BRITISH AVONIAN CONODONT FAUNAS 

Spathognathodus ziegleri sp. now 
Plate 4, figs. 5a-8d 

non 1934 Spathodus spinulico status E. R. Branson : 305, PL 27, fig. 19 [= S. sulciferus]. 

1956 Spathognathodus spinulicostatus (E. R. Branson) Bischoff & Ziegler : 167, PL 13, 

fig- 7- 

1957 Spathognathodus spinulicostatus spinulicostatus (E. R. Branson) Bischoff : 57, pi. 

4. fi g- 27- 
1957 Spathognathodus spinulicostatus spinulicostatus (E. R. Branson) Ziegler in Fliigel 

& Ziegler : PL 1, fig. 14. 
r 959 Spathognathodus spinulicostatus spinulicostatus (E. R. Branson) Helms : PL 3, 

figs. 12a, b. 
i960 Spathognathodus spinulicostatus spinulicostatus (E. R. Branson) Remack-Petitot : 

261, fig. 4. 
i960 Spathognathodus spinulicostatus spinulicostatus (E. R. Branson) Dvorak & Freyer : 

PL 2, fig. 8. 

1961 Spathognathodus spinulicostatus spinulicostatus (E. R. Branson) Freyer : 87, 88, PL 6, 
fig. 145, text-fig. 146. 

1962 Spathognathodus costatus spinulicostatus (E. R. Branson) Ziegler : 108, PL 14, 
figs. 11-18. 

1965 Spathognathodus spinulicostatus spinulicostatus (E. R. Branson) Spasov : 102, PL 
3. figs- 13. 17- 

Derivation of name. This is named in honour of Dr. W. Ziegler. 

Diagnosis. Spathognathodus with subdued oral denticulation. Anterior blade 
deep, but narrowing posteriorly, oral surface being flat. Strong development of 
accessory lateral denticles, up to 13 in number, on outer side of unit. On opposite 
side, posterior end of unit also marked by development of up to 7 smaller lateral 
denticles, giving whole posterior part an asymmetrical platform-like development. 
Basal cavity strongly laterally expanded, but lanceolate in basal outline. 

Material. Holotype X 403, Paratypes X 402, X 404, X 437 (all figured). 

Type locality and horizon and range. Honnetal, West Germany to VI Zone- 
Upper costatus Zone, roadside cutting (Ziegler 1962). 

Description. In lateral view the anterior blade is deep but straight, the oral 
surface bearing a series of reduced even denticles, only the anterior 3 or 4 of which 
have sharply defined apices. There is a tendency for the depth of the anterior blade 
to decrease towards the basal cavity, but the oral edge is straight. Behind the basal 
cavity there is a marked reduction in depth of the unit as seen in lateral view. The 
aboral edge remains more or less straight, but the oral surface slopes down to meet it 
in a relatively straight line. Its oral edge makes an angle of about 160 ° with the oral 
edge of the blade. The posterior end is spatulate to bluntly-pointed in lateral view. 
The basal cavity is a conspicuous feature when seen in lateral view. The oral 
posterior surface of the unit bears a series of low irregular denticles developed lateral 
to the main blade, but clearly visible in lateral view. These denticles, are developed 
on the inner lateral face of the unit. In outer lateral view the unit is broadly 
si miliar. 

In oral view the most striking feature of the unit is the development of up to 13 



BRITISH AVONIAN CONODONT FAUNAS 239 

laterally expanded denticles developed on the outer (convex) side of the main blade. 
These are barely visible in lateral view, but are conspicuously elongated blunt 
denticles in oral view. On the inner (concave) side posterior to the basal cavity, there 
is a series of up to 7 broadly similar denticles developed. The two sets of denticles 
tend to form a more or less continuous ridge across the posterior platform which they 
produce, although in some specimens they are arranged at such an angle to one 
another to give an arrow-like oral view. The basal cavity is conspicuously laterally 
expanded in oral view, the inner end of its long axis, which lies oblique to the main 
axis of the unit, lying anterior to that of the outer side. 

In aboral view the cavity is laterally expanded, the greatest width lying near its 
anterior end. It is shallow and asymmetrical and tapers more or less uniformly 
towards the posterior termination of the unit, having an overall lanceolate lachry- 
form outline, the anterior end being rounded. 

Remarks. This species differs from S. bischoffi in the development of an accessory 
row of posterior lateral denticles. Like that species, no mirror images of forms are 
known. In this the two species resemble many species of the genus Pseudopoly- 
gnathus, to which both are closely related in their overall morphology. 

Spathognathodus sp. A 

Plate 4, figs. I2a-c 

Material. 4 specimens : figured, X 405. 

Range. North Crop KL 3-KL 5. 

Description. The unit is arched, relatively short and deep. The major denticles 
or pair of denticles occur in the anterior quarter, being massive, tall, and laterally 
compressed. The anterior blade occurs anterior to this denticle and is formed of 
denticles developed in a fan-like manner on both the oral and anterior faces of the 
unit. The median part of the blade is fairly level, but the posterior part decreases in 



KrcO*™">%/YM 



Fig. 47. The development of Pseudopolygnathus postinodosus from a spathognathodid 
ancestor by addition of lateral denticles. 



2 4 o BRITISH AVONIAN CONODONT FAUNAS 

height rapidly near the posterior termination. The aboral outline of the unit is 
arched, the basal cavity being elongate and without flared lips. 

Remarks. This species appears to be dissimilar to all other described species of 
spathognathodids, although it is closest to 5. crassidentatus. 

Spathognathodus sp. B 

Plate 7, figs. 8a-c 

Material. 4 specimens : figured, X 406. 
Range. North Crop ZLA 5, Avon Gorge Z 34-C 7. 

Description. The bar is fairly massive being highest anteriorly, with the height 
decreasing regularly to the posterior ; the posterior termination is broken. The 
anterior-aboral portion of the blade is extended anteriorly as a short flattened 
process. The denticles, at least 17 in number, are laterally compressed and fused 
over the majority of their length. One lateral denticle occurs immediately anterior 
to the anterior margin of the cavity, and reaches the height of the main blade 
denticles. The aboral profile of the unit is not straight, the cavity tending to arch 
the posterior part upward. 

In aboral view the cavity is elongate and moderately flared, extending as a groove 
for a short distance posteriorly and anteriorly. 

Remarks. This form is probably a pathological variant of 5. cf. robustus, the 
lateral dentition placing it in an intermediate position between this and Pseudopoly- 
gnathus sp. 

Spathognathodus sp. nov. 
Plate 6, fig. 9 

Material. 15 specimens : figured, X 518. 
Locality and horizon. Avon Gorge. Sample Z 19. 
Range. Avon Gorge Z 13-Z 19. 

Description. A spathognathodid characterized by finely developed oral denticu- 
lation on a bar which is deep and protruding antero-aborally, becoming shallower 
towards its posterior end. The bar is strongly recurved in its posterior half. The 
basal cavity is strongly expanded laterally, and one or more lateral denticles are 
developed on the oral edge. The whole unit tends to be gently curved in a horizontal 
plane, and is clearly transitional towards a pseudopolygnathid condition. 

The basal bar is deepest anteriorly, and the anterior edge and antero-aboral 
margin make an angle of about 70 ° with one another, so that the antero-aboral 
angle protrudes strongly when seen in lateral view. The basal bar decreases in 
depth posteriorly. The anterior third has a straight aboral margin, but the posterior 
two thirds tend to be gently but continuously arched. The posterior end is bluntly 
spatulate. The oral surface bears a series of closely spaced acicular denticles, 
of which only the apices tend to be discrete. They are long, slender, and subequal 



BRITISH AVONIAN CONODONT FAUNAS 



241 



in length. Single accessory lateral denticles are developed in the anterior half on 
each side of the blade. 

The basal cavity is situated slightly posterior to the mid-point of the unit. It is 
very strongly flared laterally and shows a clear tendency to a pseudopolygnathid 
development, but the cavity itself, in spite of its wide flaring lips, tends to be small. 
It extends anteriorly and posteriorly as a shallow groove. The whole unit is gently 
bowed inwards in a horizontal plane. 

Genus TAPHROGNATHUS Branson & Mehl 
1 94 1 Taphrognathns Branson & Mehl : 181 (non Welles 1947). 
Type species. Taphrognathus varians Branson & Mehl. 

Taphrognathus varians Branson & Mehl 
Plate 13, figs. 4a-5d 

1940 Taphrognathus varians Branson & Mehl : 182, PI. 6, figs. 27-33, 35-40. 

1944 Taphrognathus varians Branson & Mehl ; Branson & Mehl : 246, PI. 94, figs. 66-68. 

1947 Taphrognathus varians Branson & Mehl ; Cooper : 92, PI. 20, figs. 14-16. 

1963 Taphrognathus varians Branson & Mehl ; Rexroad & Collinson : 21, PI. 1, figs. 18-20, 22. 

1965 Taphrognathus varians Branson & Mehl ; Rexroad & Collinson : 24, PI. 1, figs. 30-32. 

Material, ii specimens : figured, X 408, X 407. 



Anterior blade 




Posterior platform 



Basal cavity 



LATERAL VIEW 



Carina 



Median 
trough 




Posterior 
carina 



-Anterior blade 



Basal cavity 



Posterior platforr 



ORAL VIEW ABORAL VIEW 

Fig. 48. Taphrognathus sp. showing morphological terms used in the text. 



242 BRITISH AVONIAN CONODONT FAUNAS 

Range. Avon Gorge S 45-S 58. 

Description. The distinctive feature of this species is its general elongate form 
and its median anterior blade. This is continued posteriorly for a short distance on 
the platform as a short carina. The median trough is narrow but deep, and the 
whole platform is conspicuously lanceolate in oral view, with straight or only gently 
convex lateral margins and a conspicuously pointed posterior end. The posterior 
median part of the platform bears a nodose to sharp, short carina, which extends only 
a short distance onto the platform beyond the posterior end, but is also extended 
posteriorly beyond the termination of the platform proper. The blade tends to be 
rather long, with fused denticles. The platform is smooth and V-shaped, and rela- 
tively deep in relation to its width. It has regularly and bluntly crenulate lateral 
margins and the whole platform tends to decrease in width aborally.so that theaboral 
edge at the posterior end is more or less sharp. There is an elongated aboral cavity 
below the anterior third of the platform which is shallow and flaring and more or less 
symmetrical. It is extended anteriorly and posteriorly as a thin, slit-like excavation. 

The anterior blade is deeper than the adjacent part of the posterior platform and 
the denticles are bluntly tipped and coalesced. 

The present specimens show some variation in the degree of posterior constriction, 
in the development of the posterior carina, and in the form of denticulation of the 
anterior bar. 

Remarks. Rexroad & Collinson (1963 : 20) have shown that the genus Taphro- 
gnathus and the genus Cavusgnathus are closely related and that in some faunas 
transitional forms between these two genera can be seen. In our faunas transitional 
forms are also found (PI. 13, figs. 1-3C). The medial blade of Taphrognathus appears 
to move to take up an outer lateral position. However, since the blade is not 
completely lateral, it is difficult to determine whether these specimens belong to the 
genus Taphrognathus or to the genus Cavusgnathus. We have followed Rexroad & 
Collinson in placing them as transitional species between the two genera. They can 
be seen to be transitional, not only in the form of the anterior blade, but also in the 
general outline of the cavity, and in the reduction of the posterior carina. 

Gen. nov. A sp. 
Plate 25, figs. 6a, b 

Material, i specimen : figured, X 409. 

Locality and horizon. North Crop. Sample ZLA 6. 

Range. North Crop ZLA 6. 

Description. The unit is of a hibbardellid type, but the anterior arch is 
separated from the apical denticle by a short, denticulate, anterior bar. The anterior 
arch is broken, but can be seen to be denticulate. The apical denticle is massive, sub- 
circular in cross-section and is curved posteriorly. The posterior bar is thin and 
finely denticulate. 

In aboral view the unit is excavated, the basal cavity running from the apical 



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DUN 50 



1 



Fig. 57. Chart to show the ranges of conodont species in the Dunbar succession. Samples 
DUN 50-71, Long Craig Upper Limestone : DUN 72-82. Skateraw Limestones : DUN 
84, 85, Chapel Point Limestone : DUN 86, Dryburn Foot Limestone : DUN 87, 88, 
Barnes East Limestone. 



=Ui 



— "_ 5 5 S 



-*=> = 

i = ■: --c 






_l ! 1 1 1 \ 1 1 1 !_ 



BRITISH AVONIAN CONODONT FAUNAS 243 

denticle anteriorly to the anterior arch beneath the anterior bar, and posteriorly to 
where the posterior bar is broken. 

Remarks. This form is unlike any other described conodont genus. 

Gen. nov. B. sp. 
Plate 25, figs, 7a, b 

Material. 1 specimen : figured, X 410. 

Range. Farlow ORZ 1. 

Description. This specimen is one of problematical affinities ; its essential 
features are that it has a conspicuous, elongated, main denticle, which is subtriangular 
in cross-section, with a more or less sharp anterior edge. Its anterior aboral margin is 
very flat, but has a narrow slit extending for a minute distance up the median part of 
the face. It is recurved posteriorly, even though there is no posterior bar. Its base 
is very thick-lipped and is regularly expanded as a relatively wide and deep cavity. 
It appears that this anterior denticle is complete, though this is not certain. On the 
outer lateral face, there is an anterior aboral process which makes an angle of about 
90 ° with what would be the line of the posterior bar, and it is also depressed in a 
vertical plane. Its anterior face is very convex in anterior view, and its anterior 
distal end is straight-edged, with a sharp antero-aboral corner, but this is fractured in 
the specimen. Its oral surface bears 3 denticles, of which the two innermost are 
massive, with bluntly formed lateral edges and strongly convex anterior and posterior 
faces. The denticle at the distal end is conspicuously smaller than the other two, 
and the interior denticle, although very broad at the base, divides distally to give 2 
separate denticles. There is a tendency for germ denticles to develop between the 
larger denticles. The posterior lateral face of the anterior aboral process is flat and 
the base is continuously excavated. 

Remarks. The fact that this specimen appears essentially complete makes it 
impossible to assign it to any existing genus. It may, in fact, represent a new one, 
but it is possible that it is a broken specimen of Hindeodella corpulenta. 

VII. SUMMARY AND CONCLUSIONS 

(a) Scope of the present work 

During the last decade, studies in both Germany and the United States have 
demonstrated the potential value of conodonts in Carboniferous and Devonian strati- 
graphical correlation. The present study represents a comprehensive description of 
the conodont faunas of the British Lower Carboniferous, and a detailed analysis of 
their stratigraphical distribution. This has been used to erect a zonal scheme, by 
means of which a more precise correlation has been established between sections in 
each of the main British Carboniferous depositional provinces than any yet available 
on the basis of other faunal groups. Intercontinental correlations are also suggested. 



244 BRITISH AVONIAN CONODONT FAUNAS 

(b) Previoiis research 

A critical review of previous research on Carboniferous conodont faunas is given, 
together with a review of the present status of Carboniferous stratigraphical correla- 
tion (p. 17). 

(c) Collecting localities 

Samples have been collected from each of five major depositional areas. This has 
provided an indication of the degree of variability of conodont faunas both within 
and between depositional basins. In all some 3! tons of limestone has been 
processed. 

Avon Gorge, Bristol 

Detailed sampling of this area has involved the digestion of some 189 ' major ' 
rock samples, most of them about 10 lbs in weight. Every 10 ft. of the section 
was sampled, and these samples were supplemented in critical parts of the succession 
by others taken at 5 ft. and 2 ft. intervals. The stratigraphy of the collecting areas 
is described in detail (p. 18). 

North Crop of the South Wales Coalfield 

A series of eleven localities in Brecknockshire and Monmouthshire was used to 
construct a composite Lower Carboniferous section, and small collections were made 
from Gower and Pembrokeshire. The middle part of the Avonian succession is 
generally not fossiliferous in this area, but the higher parts of the Dibunophyllum 
Zone have been used to complement the zonal scheme for the lower part of the 
section, established in the Avon Gorge. 

Shropshire 

The thin development of the Z and K Zones at Farlow and Oreton have yielded 
well-preserved faunas (p. 25). 

Yorkshire 

Sampling of the Yoredale succession in the type area has provided material for a 
reconnaissance survey of Yoredale conodont faunas. They show close similarities to 
those of the higher zones from the South Western Province. 

Scotland 

Extensive collections have been made from Dunbar, Roxburgh, Midlothian, Fife, 
Ayrshire and Argyll. All the major limestones in the succession were sampled, some 
at intervals of six inches, and most yielded well-preserved faunas. 

(d) Methods of study 

Most of the 25,000 specimens which form the basis of the study were extracted by 
digestion of limestone in 8 % acetic acid. Methods of preparation and photography 
are described. The abundance of conodonts in each sample has been recorded 
(Figs 59-92)- 



BRITISH AVONIAN CONODONT FAUNAS 245 

(e) Stratigraphic ranges 

The precise ranges of all conodont species recovered are shown by range charts 
(Figs. 49-58). The ranges of the more stratigraphically useful genera and species 
are described. Patrognathus gen. nov. is confined to the K Zone. Clydagnathus 
gen. nov. is found in the K and Lower Z Zones of the North Crop and Shropshire, but 
is rare in large faunas of the same age from the Avon Gorge. Siphonodella is very 
rare in the Avonian, being confined to the Upper K Zone (p. 32). 

Pseudopolygnathus extends from the basal K to the Ci Zone. It is represented by 
numbers of short-lived species and is abundant in the Avon Gorge, but less common 
in the North Crop (p. 32). 

Gnathodus is a long-ranging Avonian genus, but individual species are valuable for 
correlation in the Z, C and D Zones (p. 34). Spathognathodus is equally long- 
ranging, but several short-lived species are valuable index fossils in various portions 
of the succession. 

Polygnathus ranges from the K to the top of the Ci Zone, and is represented by a 
number of species. Mestognathus extends from the Ci to the D2 Zone (p. 35), while 
Cavusgnathus is most characteristic of the C2, S and D Zones. Taphrognathus is 
restricted to the Upper S2 Subzone (p. 35) in the south west, but occurs in the C 
Zone of Roxburghshire. 

Fourteen conodont assemblage zones are established 

(f) Geographic variation 

Our study shows several striking examples of what appear to be geographical 
differences in contemporaneous conodont faunas. These include representatives of 
the genera Siphonodella (p. 32), Pseudopolygnathus (p. 32), and Clydagnathus 
(p. 32) among others. These differences reflect variation not only between faunas 
separated by intercontinental distances, but also between faunas from the same 
general depositional basin (e.g. the Avon Gorge and the North Crop). The degree of 
such geographic variation is shown to be often greater than that generally admitted 
by most conodont workers, and is an important consideration in stratigraphic 
correlation. The absence of certain conodont genera and species from some areas 
may represent either the absence of one or more groups of conodont-bearing animals 
(conodontifers) of whatever taxonomic level, or the homoeomorphic replacement of 
certain conodonts within the same broad type of natural assemblage of the cono- 
dontifers. 

(g) Correlation within the British Avonian 

Avon Gorge-North Crop 

The broad equivalence of Vaughan's coral-brachiopod zones as recognized in these 
two areas is supported by a comparison of the conodont faunas. The basal K strata 
of the North Crop are probably slightly younger than those of the Avon Gorge. The 
Upper K Zone of the Avon Gorge is equivalent to the uppermost K and basal Z Zones 
of the North Crop (p. 46). 



2 4 6 



BRITISH AVONIAN CONODONT FAUNAS 




Abundance fnrtor = Total no.of specimens 
Total weight o( sample 



Total weight of sample 
in kilograms 



Fig. 59. Lithological section of the Cleistopora Zone in the Avon Gorge showing the 
abundance factor of conodonts in each sample, and the total weight of each sample 
dissolved in acetic acid. Samples K1-K17 were collected in the riverside section of the 
Avon Gorge (ST 556746). Samples K 18-K 21 were collected in the quarry 1 of the Avon 
Gorge (ST 557745), see Text-fig. 2. 



BRITISH AVONIAN CONODONT FAUNAS 



247 



253 
111 



•FTT - 



T7T 



CC 



TTTT 



3^E 



"57^ 



j. : d ; j, 



3^ 



5^c: 



5SJ 1 



At A 



i , ; i .' i 



i , A t 



3^-, i , ^ 



l -y l "V I - 



SE 



JgE 



& e> 




""""■' 



ft^v^M/ ■yv-,^ 



: 



I' 



■I 



Abundancefactor = Total no.of specimens 
Total weight of sample 



Total weight of 
sample in kilograms 



Fig. 60. Lithological section of the Lower and Upper Zaphrentis Zone in the Avon Gorge 
showing the abundance factor of conodonts in each sample, and the total weight of each 
sample dissolved in acetic acid. Samples Z i-Z 10 were collected in Quarry 1 (ST 557745), 
Samples Z 11-Z 20 were collected in the Black Rock Quarry (ST 561747) and Samples 
Z 21-Z 33 were collected in Quarry 2 (ST 561747). 



248 



BRITISH AVONIAN CONODONT FAUNAS 




Abundance factors TotQl no of specimens Total weight of 

Total weight ot sample sample in kilograms 



Fig. 61. Continuation of the lithological section of the Upper Zaphrentis Zone (y Beds) 
in the Avon Gorge showing the abundance factor of conodonts in each sample dissolved 
in acetic acid. Samples Z 34-Z 38 were collected in Quarry 2 (ST 558745). 



BRITISH AVONIAN CONODONT FAUNAS 



249 




zzz 



±m± 



i»i-i 



MlTM'A 



h 1 ■ 1 



1~7~T 



I \ I 



est 



1/1 / 



Si 



-i-/-i-r 




Abundance foctor = Totol no of specimens 
Total weight of sample 



Total weight of 
sample in kilograms 



Fig. 62. Lithological section of the Lower Caninia Zone in the Avon Gorge showing the 
abundance factor of conodonts in each sample dissolved in acetic acid. Samples C i-C 1 1 
were collected in the Railway Cutting (ST 559745) and Samples C 12-C 25 in Quarry 3 
(ST 560744). 



250 



BRITISH AVONIAN CONODONT FAUNAS 



C39- ?^-y 











•/j/jf/jfrmTj} 



warn 

mm 



Bl I I I I I I I I I I I 



Abundance factor = Total no of specimens 
Total weight of sample 



Totol weight of sample 
in Kilograms 



Fig. 63. Lithological section of the Upper Caninia Zone in the Avon Gorge showing the 
abundance factor of conodonts in each sample dissolved in acetic acid. Samples were 
collected from the roadside exposure (ST 562746). 



BRITISH AVONIAN CONODONT FAUNAS 



251 



WrT' 



E3E; 



Trr 



a* 



TTT- 





Abundance mm nr- Total no of specimens 
Total weight of sample 



Total weight of 
sample in Kilograms 



Fig. 64. Lithological section of the Lower and Upper Seminula Zone in the Avon Gorge 
showing the abundance factor of conodonts in each sample, and the total weight of 
each sample dissolved in acetic acid. The samples were collected in the Great Quarry 
(ST 56374°)- 



2 5- 



BRITISH AVONIAN CONODONT FAUNAS 




i o IQIOICJ I 




I 1 U 11 I 



Abundonce factor: Totol no o( specimens 
Total weight of sample 



Total weight of 
sample in kilograms 



Fig. 65. Continuation of the lithological section of the upper part of the Seminula Zone 
in the Avon Gorge showing the abundance factor of conodonts in each sample dissolved 
in acetic acid. Samples S 22-S 30 were collected from the Great Quarry (ST 563740) 
and Samples S 31-S 50 from the riverside exposure (ST 562737). 



BRITISH AVONIAN CONODONT FAUNAS 



^TT 



III 





i 't !' t| i 

"VS I T . 



/ 



Abundonce Toctor = Total no.of specimens 
Total weight of sample 



Total weight of 
sample in kilograms 



253 



Fig. 66. Continuation of the lithological section of the uppermost part of the Seminula 
Zone and Concretionary Bed in the Avon Gorge showing the abundance factor of cono- 
donts in each sample dissolved in acetic acid. Samples S 51-S 72 were collected from 
the riverside exposure (ST 562737). 



254 



BRITISH AVONIAN CONODONT FAUNAS 




Abundance factor = Total no of specimens 
Total weight of sample 



Total weight of 
sample in kilograms 



Fig. 67. Lithological section of the Lower Dibunophyllum Zone in the Avon Gorge showing 
the abundance factor of conodonts in each sample dissolved in acetic acid. Samples 
D i-D 9 were collected from the roadside exposure (ST 564737). 



BRITISH AVONIAN CONODONT FAUNAS 



255 



021 - :'-^ -r. 



D20- '.tS-Jt 



P17- I I I ~T 



013 -~J 



T-p..i>-f.o.'!? 



Ill 



11 1 



P?^ 



ffi^ 



r^V-r 



m 



-i^Cn 



1 . ' ; 1 . 1- 



012 - ^ g 



: i , t , r 



W 



TVT 



IT 



III 



Abundance factor= Total no, of specimens 
Total weight of sample 



5 10 

TJTI 







A 




VMMA* 



Total weight of 
sample in kilograms 



Fig. 68. Continuation of the lithological section of the Dibunophyllum Zone in the Avon 
Gorge showing the abundance factor of conodonts in each sample dissolved in acetic acid. 
Samples D to D 22 were collected from the roadside exposure (ST 564737). 



256 



BRITISH AVONIAN CONODONT FAUNAS 




Abundance fnrtnr- Total no. of specimens 
Total weight of sample 




% 



^iiiln 



Total weight of 

sample in 

kilograms 



Fig. 69. Lithological section of the upper beds of the Dibunophyllum Zone in the Avon 
Gorge showing the abundance factor of conodonts in each sample dissolved in acetic 
acid. Samples D 23-D 27 were collected from south of Bridge Valley Road (ST 564736). 



BRITISH AVONIAN CONODONT FAUNAS 



257 



O 5 10 15 20 




,„ Total no. of specimens Total weiqhtof sample 

Abundance factor = . ki ? nnr .„ m . 

Total we ght of sample ' n kilograms. 



Fig. 70. Lithological section of the K Zone of the North Crop of the South Wales Coalfield 
showing the abundance factor of conodonts in each sample, and the total weight of 
limestone dissolved. For details of collecting localities see Fig. 7 and also p. 25. 



25S 



BRITISH AVONIAN CONODONT FAUNAS 




Abundance factor , Total no. of specimens 
Total weight of sample 



Total weight of sample 
in kilograms 



Fig. 71. Lithological section of the Z and S2 Zones of the North Crop of the South Wales 
Coalfield showing the abundance factor of conodonts in each sample, and the total weight 
of limestone dissolved. For details of collecting localities see Fig. 7 and also p. 25. 



BRITISH AVONIAN CONODONT FAUNAS 



259 



75 



50 



25 



L o- 1 - 



CYD 




20 



40 



60 



80 



Abundance foctor = Total no. of specimens 
Total weight of sample 



-J 



5 10 15 
1 11 1 1 J I 1 1 I 



I 

I 
1 

Sfl i 1 1 1 1 1 il 11 1 



10 15 



Total weight of sample 
in kilograms 



Fig. 72. Lithological section of the D2 Subzone of the North Crop of the South Wales 
Coalfield showing the abundance factor of conodonts in each sample, and the total weight 
of limestone dissolved. For details of collecting localities see Fig. 7 and also p. 33. 



26o 



BRITISH AVONIAN CONODONT FAUNAS 



5 10 15 




Abundance factor: Total noof specimens 
Total weight of sample 



Total weight of somple 
in kilograms. 



Fig. 73. Lithological section of the D3 Subzone of the North Crop of the South Wales 
Coalfield showing the abundance factor of conodonts in each sample, and the total 
weight of limestone dissolved. For details of collecting localities see Fig. 7 and also p. 23. 



BRITISH AVONIAN CONODONT FAUNAS 



261 



5 10 15 20 



I — »0 7— ■ 



l_78 4 



41 2 

6 '2" 



a: 



FAR 7 



fc-=i/rV 



FAR7A 



i 



6lt COVERED 



IFAR6 g 



6 ft COVERED 



FAR 5 


T^T ^( 






T^, 5 ^ 





20 ft COVERED 




Abandonee factor: Total no of specimens 
Total weight of sample 




23 

1 



TTTTTTTTTT 









1 1 1 1 1 1 1 1 1 1 1 1 1 



5 10 15 20 



Total weight of sample 
in kilograms 



Fig. 74. Lithological section of the Cleistopora Zone at Farlow, Shropshire (Map reference 
SO 642808), showing the abundance factor of conodonts in each sample and the weight 
of each sample dissolved. 



262 



BRITISH AVONIAN CONODONT FAUNAS 




TTT 



urn 




3L_L 




Abundance ■ 



No of specimens 
Total weight of sample 



Total weight of 
sample in 
kilograms 



Fig. 75. Lithological section of the Zaphrentis Zone in Oreton Quarry, Shropshire, (SO 

648806). 





Abundance factor: Total no. of specimens 
Total weight of sample 



Total weight of sample 
in k i I o g ra m s 



Fig. 76. Composite lithological section through the Yoredale Group (Hawes Limestone 
to base of Simonstone Limestone) in the Gayle Beck — Hawes area (34/864883). 



BRITISH AVONIAN CONODONT FAUNAS 



263 





Abundance factor = 



Total no of specimens 
Total weight of sample 



Total weight of 
sample in 
kilograms. 



Fig. 77. Composite lithological section through the Yoredale Group (base of Simonstone 
Limestone to the top of the Five Yard Limestone inclusive) in the Snaizeholme — Hawes 
area (34/815840). S. Ls. = Simonstone Limestone : F.Y. Ls. = Five Yard Limestone. 



T~7 



33 



BEE 



'.''.'"^"j - '.* 



gUVLHLU 



eovcprn 



COVERED 



>M I I I I I II I I I I I 



I I II I I I I I I I I I I 



Abundance fnrw- Totol no. of specimens 
Total weight of sample 



Total weight of sample 
in kilograms. 



Fig. 78. Composite lithological section through the Yoredale Group (top of the Five 
Yard Limestone to the top of the Underset Limestone inclusive) in the Snaizeholme — 
Hawes area (34/815840). T. Y. Ls.=Three Yard Limestone : U. Ls. = Underset 
Limestone. 



264 



BRITISH AVONIAN CONODONT FAUNAS 



-10 



-0 - 1 - 




5 10 15 20 

1 1 1 hum 1 1 11 1 1 1 i i i 



_i_ 



j_ 



11 1 1 1 1 11 1 li 11 1 111 1 1 



20 



Abundance foctor= 



40 60 80 

Totol no of specimens 
Total weight of sample 



3 5 10 >5 20 

Total weight of sample 
in kilograms. 



Fig. 79. Lithological section of part of the Lower Limestone Group in the Dunbar area : 
the Long Craig Upper Limestone, showing the abundance factor for each sample and 
the weight of each sample dissolved. For localities see p. 30. 



BRITISH AVONIAN CONODONT FAUNAS 



265 




10 15 20 

Abundance factor: Total no. of specimen. Totol we.ght of sample 

Total weight of sample in kilograms. 



Fig. 80. Lithological section of part of the Lower Limestone Group in the Dunbar area : 
the Scateraw Lower Limestone to the Scateraw Upper Limestone, showing the abundance 
factor of each sample and the total weight of each sample dissolved. For localities see 
p. 30. 



266 



BRITISH AVONIAN CONODONT FAUNAS 



eo'y 






r.: T -.:T. 

X.'-i.'. XI 
-..! 

r- ■ ■ t- 






z>- 


DUN 88 








i i i 






'iii 






i ' i i 








■ ' ' ■ ' 






cnuj-i 


DUN 87 


1 i ' i ' i 






i i i 










t r 










T 










■T---T-- 

"[ TV 




70 






wwwvwi 




i 

28 






.T.-p.'. T 

T X 

T? T 

T- ' • T 
r - ... 

T--..V 

T T" 






crOoo 

QltJ 


DUN 8G 








II 






I I 


















III 






1 1 1 


i 




| 11 










TT'T- 










tL'"ti: 






L 




Til' T U 




-20 


D 
D 
X 

s 

J 

z 

o 
/> 




TH" T l' 

ti:"t-i; 

T^"T1' 
T"— " *T ^' 

ti.-t .:■ 








T-TS 






_j 




TUJT^- 






K 




T T 
















s 




T1L"T".1" 











T^l'TV.!" 






_l 




T^'T'M'1 

T 1 1 

=X4 


f 

r 

r 

- 


10 


i/i 

_i 

»- 
z 


DUN 85 


'■'■'■ 






l l 1 






i i 1 






I'll 






1 1 1 






III 






III 






ill 






III 






',',', 






o 




1 ' 1 ' 1 ' 






III 






-1 
LI 
0. 
< 

X 

u 




1 1 1 






III 












DUN 84 


'■ ■ ■ '■ 


-f 




l l l 






III 






1 1 ' 1 ' 






l l l 

!■!■!■ 










i * i ' i ii 

iii 1 
.,.1,1,1,1 

1 T 1 








, -X • 








•-!-■'• T 








... ., . j 








■-T-'- ■ t y~ 


-0 ■■ 






:- x:^ 






.p. •/ 



5 10 
MIIIIMI 



20 40 60 80 

Abundance factor ; Total no. of specimens 
Total weight ol sample 



Total weight of sample 
in kilograms 



Fig. 8i. Lithological section of part of the Lower Limestone Group in the Dunbar area : 
the Chapel Point Limestone to the Barness East Limestone, showing the abundance 
factor of each sample and the weight of each sample dissolved. For localities see p. 30. 



BRITISH AVONIAN CONODONT FAUNAS 



267 



-60 



-50 



-40 



-30 



-20 



-10 




5 10 15 



20 




40 



10 15 



Abundance foctor= Totol no of specimens Total weight of sample 
Total weight of sample in kilograms 



Fig. 82. Lithological succession of part of the Lower Limestone Group in Midlothian : 
the " Gilmerton " Limestone, showing the abundance factor of each sample and the 
weight of each sample dissolved. This limestone may not be the true Gilmerton 
Limestone (see p. 50). For localities see p. 30. 



.'68 



BRITISH AVONIAN CONODONT FAUNAS 




5 10 
M"imi|iiii 



U i I i i 1 1 



20 40 60 80 5 10 15 



Ah..r,H/-.r,^4. « „ ^ i « . Total no of specimens 

Abundance factors — 

Total weight of sample 



Total weight of sample 
in kilograms 



Fig. 83. Lithological section of part of the Lower Limestone Group in Midlothian : 
the North Greens Limestone, showing the abundance factor for each sample and the 
weight of each sample dissolved. For localities see p. 30. 



BRITISH AVONIAN CONODONT FAUNAS 



269 



r35 



■30 



-20 



10 



LO 




5 10 15 

I I I M 1 1 | 1 M I J 




20 



40 



60 



80 



*t..„^_„,_ („,. Total no of specimens 

Abundance factor = 

Total weight ot sample 



5 10 15 



Total weight of 
sample in 
Kilog rams 



Fig. 84. Lithological section of part of the Lower Limestone Group in Midlothian : the 
Bilston Burn Limestone, showing the abundance factor and total weight of sample 
dissolved for each sample. For localities see p. 30. 



270 



BRITISH AVONIAN CONODONT FAUNAS 



L - 1 - 




5 10 1! 



JM I I I I 1 I I I I 1 I I 

I 




20 



40 



60 



80 5 10 15 



Abundonce foctor = 



Totol no of specimen s 
Total weight of sample 



Total weight of sample 
in k i I o g ra m s . 



Fig. 85. Lithological succession of part of the Calciferous Sandstone Series of East Fife, 
showing the fossiliferous limestones in the lower part of the succession. Coast section 
from Hurlet Limestone near Coalfarm to Anstruther (NO 548027). Sample numbers 
refer to detailed section given by J. W. Kirkby in Geikie (1902), p. 77 ff. 



BRITISH AVONIAN CONODONT FAUNAS 



271 



-2 5 

- 



-20 




SI 3 


O *~ 

Z 


1 


1 


1 ' 


1 l( 




V' v \ 1 " 

v//. 






10 15 



^A 



60 



100 



5 10 15 



abundance loctor = Totoi naofspecimens 
Total weigh! 01 sample 



Total weight of sample 
in kilograms. 



Fig. 86. Continuation of coast exposure of Fig. 85. Lithological section of part of the 
Lower Limestone Group in East Fife : Hurlet and Hosie Limestones, showing abundance 
factor for each sample and weight of each sample dissolved. 



-7- 



BRITISH AVONIAN CONODONT FAUNAS 




1 1 ii 1 1 1 1 1 1 1 



i i ' ■ 



Abundance factor 



Total no of specimens 
Total weight of sample 



Total weight of 

sample 

in kilograms 



Fig. 87. Lithological section of part of the Lower Limestone Group in North Ayrshire : 
the Dockra Limestone, showing abundance factor for each sample and weight of each 
sample dissolved. For localities see p. 30. 




5 10 
1 1 1 mil ii 



20 



40 



60 



80 



Abandonee factor; Tot °' no. of specimens 
Total wel qht of sample 



10 



Total weight of sample 
in kilograms 



Fig. 88. Lithological section of part of the Calciferous Sandstone Series in North Ayrshire, 
showing the abundance factor of each sample and the total weight of each sample 
dissolved. For localities see p. 30. 



BRITISH AVONIAN CONODONT FAUNAS 



273 





11 111 1 



Abundance factor = 



Total no. of specimens Total weight of sample 



Total weight of sample 



in kilograms 



Fig. 89. Lithological section of part of the Lower Limestone Group of North Ayrshire : 
the Hosie Limestone, showing the abundance factor for each sample and the weight of 
each sample dissolved. For localities see p. 30. 



*74 



BRITISH AVONIAN CONODONT FAUNAS 




5 10 13 20 

I I I I 1 1 I II | I I I I I I I I I 



I I I I I I I | I I I I I I I I I 



ak. „,■„„,„ <„- ( „, Total no. of specimens 

Abundance factor = c 

Total weight of sample 



Total weight of sample 
in kilograms 



Fig. 90. Lithological section of part of the Upper Limestone Group of North Ayrshire : 
the Index Limestone to the Upper Linn Limestone, showing the abundance factor for 
each sample and the weight of each sample dissolved. For localities see p. 30. 



BRITISH AVONIAN CONODONT FAUNAS 



275 



f- 40 "I— 



5 10 15 




5 10 15 



Abundance factor = Total weight of sample 

Total no. of specimens in kilograms 

Total weight oi sample 



Fig. 91. Lithological section of the Lower Algal Limestone " Series " of Harden Burn, 
Roxburghshire, (NY 517907) showing the abundance factor for each sample and the 
weight of each sample dissolved. 



276 BRITISH AVONIAN CONODONT FAUNAS 

Mid-Avonian unconformity in some places in the North Crop, and the absence of 
conodonts in others, does not allow comparisons of the middle part of the succession, 
although the uppermost Z of the Avon Gorge is younger than that of the North Crop. 
The base of the D2 Subzone corresponds in both the Avon Gorge and the North 
Crop. Few D2 or D3 conodonts have been recovered from the Avon Gorge (Figs. 
67-69). 

Shropshire 

The lowest K strata at Farlow appear to be younger than those of the Avon Gorge, 
or the North Crop. The Shropshire K Zone strata represent a very condensed 
deposit. The higher part of the K Zone at Farlow is equivalent to the Lower Z of the 
Avon Gorge. The Z Zone at Farlow represents the Spathognathodus costatus costatus- 
Gnathodus delicatus Zone. 

Yorkshire 

The lowermost Yoredale limestones (the Gayle and the Hawes) have yielded few 
conodonts. The overlying Hardraw Scar Limestone and Simonstone Limestone fall 
within the Gnathodus mononodosus Assemblage Zone, and the Middle and Five Yard 
Limestones within the Gnathodus girtyi collinsoni Assemblage Zone. 

Scotland 

A correlation is suggested between the Fife, Midlothian, Ayrshire, Dunbar and 
Glengarnock successions, and between these and the South Western Province. The 
Scottish sections all fall within the Gnathodus mononodosus or Gnathodus girtyi 
collinsoni Zones, except for the lowest part of the Ayrshire succession and the Lower 
Algal " Series " of Roxburghshire. Details of the correlations are given in Fig. 15. 

(h) Intercontinental correlation 

A critical review of North American and European Lower Carboniferous conodont 
faunas is given (p. 52), and the correlation of these with the British Avonian is 
summarized in Figs. 12, 16. The K Zone of the Avonian, represented by the two 
lowest conodont zones and by the lower part of the Spathognathodus cf. S. robustus- 
S. tridentatus Zone, is probably equivalent to the Lower Hannibal-Upper Chouteau 
succession of the Mississippi Valley (Cu I-Cu II a). This would imply a very con- 
siderable unconformity below the " Sedalia Formation " (Lower Cu II (3-y) which is 
correlated with the Polygnathus lacinatus Zone of the Upper Z2 Beds. An alternative 
correlation, based upon the first appearance of Gnathodus delicatus, would equate the 
Spathognathodus costatus costatus-Gnathodus delicatus Zone of the Middle Z Zone 
with the Upper Chouteau (Cu II a) (p. 56). The highest Z Zone is equivalent to 
the Fern Glen and lower part of the Burlington Formations (Middle Cu II (3-y). 

The Ci Subzone of the Avonian is of Upper Cu II [3-y-Lower Cu II 8 (Middle and 
Upper Burlington) age, and the C2S1 and S2 Subzones of Upper Cu II 8 age. 
(Keokuk to Lower St. Louis). 

The D] Subzone is of Cu III a age, the D2 Subzone of Cu III a-Cu III (3 age, and 
the D3 Subzone of Cu III (3-y age. 



LEGEND FOR LITHOLOGICAL SECTIONS 

CLASTIC SEDIMENTARY OTHER SEDIMENTARY ROCKS GENERAL 
ROCKS AND STRUCTURES 




o 
o o 


Gravel 




Limestone 


T 


Lithified 

formation 


1 I 




















Conglomeratic 
arkose 


tV 


Fossil-fragment 
limestone 


C 


Covered 




















Coarse-grained 
sandstone 


?i? 


Detrital 
limestone 


'///> 


Red beds 


i • i 


















3?S 


Conglomeratic 
sandstone 


91? 


Limestone 
breccia 






2 5% sand 
7 5°/. clay 


|o| 




















Calcareous 
sandstone 


o 1 o 


Oolitic 
limestone 


IS 


Lateral 
transition 


1 o | 


y 


















■ 


Slightly sandy 
formation 


® 1 © 


Pi sol it i c 

limestone 


\7 ^7 
<C7 


Chert 


l®l 


















-r~ ' • ' ' 


Siltstone 


X | X 


Crystalline 
li mestone 


^7 


Cherty 
format i on 


|x| 




















Clay 


CD | CD 


Sucrose 

limestone 


<2> 


Concretions 


1=1 




















Stratified 
clay 


y j 


Dolomite 


/! 


Algoe 


/ / 





















Argillaceous 
formation 


J / 


Dolomitic 
h mestone 


o 


Corals 


/ 1 


















=F 


Shale 


rrr 

IE 


Calcareous 
formation 


■ 




Brachiopods 


^^ 




















Thin coal bed 


^ ^ 


Marl 


6 


Fossils in 
general 




















A A 


Fine clay 


— | — 


Argillaceous 
limestone 


Y 


Bryozoa 


l-l 




















Shale lenses 


-T-r- 
• nzn 


Colcareous 
lenses 


# 


Cnnoids 




















Silt 


IX 


Dolomit ic 

lenses 
















^ 


Carbonaceous 
shale 





















Fig. 92. Composite legend for the lithological sections shown in the text. 



BRITISH AVONIAN CONODONT FAUNAS 277 

(i) Systematic palaeontology 

The total fauna described includes some 25,000 identifiable specimens, referable to 
167 species. These are described and illustrated, and their precise stratigraphical 
ranges recorded. Two new named genera, 40 new species and 13 new subspecies 
are recognized. 

(j) Detailed lithological sections and abundance figures are included for each part of 
the succession. Range charts are also provided. 

VIII. ACKNOWLEDGMENTS 

We are deeply indebted to our colleagues in the Geology Department, University 
College of Swansea, for help and advice during the course of this study. Mr. T. R. 
Owen has given us the benefit of his extensive knowledge of the Avonian rocks of 
South Wales, and has been a particular help to us in planning our collecting in that 
area. Mr. Brian Simpson has assisted us with various aspects of the technical work 
involved in the study. We owe a particular debt of gratitude to Mrs. Shirley 
Osborn and Mr. Michael Reynolds, for their patient help in rock processing, to Miss 
Sonia Kostromin for her enormous secretarial help, to Mr. Stanley Osborn for his 
skilful photography, to Mrs. Greir Lewis and Mrs Beryl Fisher who have prepared 
the text-figures, to Miss Rhiannon Watkins for typing, and to Miss Veronica Arlen 
and Mr. H. A. H. McKee for their editorial help. 

We have been greatly helped by the generous advice of a large number of friends 
in various countries, who have willingly discussed problems of systematics and 
correlation with us, and have in some cases provided topotype material for com- 
parison. We particularly wish to thank Dr. Gunther Bischoff of Gewerkshaft 
Elwerath Erdolwerke, Hannover, Dr. Charles W. Collinson of the Illinois Geological 
Survey, Dr. Raphael Conil of the Catholic University of Louvain, Professor Brian F. 
Glenister of the University of Iowa, Professor F. Hodson of Southampton University, 
Dr. John Huddle of the U.S.G.S., Washington, Dr. Huw Jenkins of Sydney Univer- 
sity, Dr. Gilbert Klapper of Pan American Petroleum Corporation, Tulsa, Oklahoma, 
Dr. M. Lys of the Institut Francais du Petrole, Dr. S. C. Matthews of the University 
of Bristol, Dr. Klaus-Dieter Meischner, of the University of Gottingen, Dr. D. Moore 
of Southampton University, Dr. Carl Rexroad of the Indiana Geological Survey, 
Dr. James W. Scatterday of the State University of New York at Geneseo, Dr. 
Trevor Walker of Long Beach College, California, Mr. R. B. Wilson of the I.G.S., 
Edinburgh, and Dr. Willi Ziegler of the Geologisches Landesamt Nordrhein-West- 
falen. 

We are also grateful for the financial support which made this study possible. 
The Department of Scientific and Industrial Research, and its successor, the Science 
Research Council, made a grant to F. H. T. Rhodes, to support a programme of 
research, of which this study forms a major part. This grant provided support for 
E. C. Druce, and R. L. Austin received a D.S.I.R. Studentship. We are also grateful 
for the support in the form of accommodation, apparatus, materials and technical 
help provided by the University College of Swansea. 



278 BRITISH AVONIAN CONODONT FAUNAS 

The completion of much of the present paper has also involved help from other 
sources which we wish to acknowledge. During 1965-66 F. H. T. Rhodes held a 
National Science Foundation Senior Visiting Scientist Fellowship at Ohio State 
University. The award of this Fellowship, and the warm hospitality provided by 
the Geology Department at Ohio State are acknowledged with deep gratitude, as 
is the typing assistance of Miss Emily Laws. 

R. L. Austin gratefully acknowledges the facilities and assistance provided at 
the University of Southampton during the past two years, and especially the con- 
tributions of Mrs. B. Gilkes and Mrs. A. Dunkley. 

The publication of the present paper owes much to the generous encouragement 
and help of Dr. H. W. Ball, Dr. W. T. Dean, Mr. E. F. Owen and Mr. H. G. Owen of 
the Palaeontology Department of the British Museum (Natural History). 



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292 BRITISH AVONIAN CONODONT FAUNAS 

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BRITISH AVONIAN CONODONT FAUNAS 



293 



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Manuscript submitted 6th March, 1967 



X. APPENDIX 



(a) Sample Register 
The following prefixes are used for sample numbers 



KL 




K Zone 


North Crop Limestone 


KSh 




K Zone 


North Crop Shale 


ZL 




Z Zone 


North Crop Limestone (ten feet samples) 


ZLA 




Z Zone 


North Crop Limestone (two feet samples) 


ZSh 




Z Zone 


North Crop Shale 


CL 




C 2 Si Zone 


North Crop Limestone 


CSh 




C2S1 Zone 


North Crop Shale 


SL 




S2 Zone 


North Crop Limestone 


1 DL 




Di Zone 


North Crop Limestone 


CYD 




D 2 Zone 


North Crop (Craig-y-Dinas) 


2DL 




D2 Zone 


North Crop Limestone 


2D Sh 




D2 Zone 


North Crop Shale 


3D 




D3 Zone 


North Crop Owen & Jones numbers 


FAR 




K Zone 


Farlow 


ORZ 




Z Zone 


Farlow (Oreton) 


HAR 




Ci Zone ? 


Harden Burn, Roxburgh (Lower Algal limestone) 


DUN 




L. Limestone Group 


Dunbar 


GILM 




Gilmerton Limestone 


Midlothian 


BIL 1-, 


\ 


Beds below North Greens Limestone 


BIL 100 + 


Bilston Burn Limestone 


Midlothian 


NGL 




North Greens Limestone 


Midlothian 


VEX 




Lower Vexhim Limestone 


Midlothian 


ANS 




Calciferous Sandstone Series 


Fife 


HOSIE 




Hosie Limestones 


Fife 


HURLET 


Hurlet Limestone 


Fife 


GO-IN 


s 






DR-IN 


Index Limestone 


Ayrshire 


LIN-L 




Lower Linn Spout Limestone 


Ayrshire 



204 



BRITISH AVONIAN CONODONT FAUNAS 



U-LIN 

BRAU 

ADOC 

GLEN 

MAC 

SCC 

GUD 

K 
Z 
C 
S 
D 
Y 



Upper Linn Spout Limestone 
Broadstone Limestone 
Dockra Limestone 
Hosie Limestones 
Lower Limestone Series 
C Zone 



Ayrshire 

Ayrshire 

Ayrshire 

Glengarnock, Ayrshire 

Macrihanish, Argyll 

Fall Bay, Gower, South Wales 



Upper Devonian Germany, Honnetal 
Upper costatus Zone to VI 

K Zone Avon Gorge Limestone 

Z Zone Avon Gorge Limestone 

C Zone Avon Gorge Limestone 

S Zone Avon Gorge Limestone 

D Zone Avon Gorge Limestone 

Yoredale Limestone Yorkshire 



Map references for all localities are given in the text-figure explanations and on p. 18-31. 



REGISTER OF FIGURED SPECIMENS 



Slide 


Nos of 


figured 


specimens 


X 


36 - 


X 


37 


X 


38 


X 


39 


X 


40 


X 


4i 


X 


42 


X 


43 


X 


44 


X 


45 


X 


46 


X 


47 


X 


48 


X 


49 


X 


50 


X 


5i 


X 


52 


X 


52 


X 


54 


X 


55 


X 


56 


X 


57 


X 


58 


X 


59 < 


X 60 



Name of Conodont 



Angulodus walrathi (Hibbard) 
sp. nov. B 
sp. nov. C 
sp. nov. C 
sp. nov. D 
sp. nov. D 

Apatognathus varians Branson & Mehl 
sp. nov. A 
chauliodus Varker 
bladus sp. nov. 
bladus sp. nov. 
scalenus Varker 
scalenus Varker 
scalenus Varker 
petilus Varker 
petilus Varker 
petilus Varker 
petilus Varker 
geminus (Hinde) 
geminus (Hinde) 
geminus (Hinde) 
geminus (Hinde) 
cf . libratus Varker 

Cavusgnathus charactus (Rexroad) 

Apatognathus sp. 



Sample Number 

KL 19 
ZLA 14 
ZLA 10 
ZLA 14 
ZLA 11 
ZLA 11 
ZLA 13 
ZLA 13 
HOSIE 2 B 
CYD 7A 
CYD 7A 
HOSIE 2 B 
HOSIE 2 B 
HOSIE 2 B 
HOSIE 2 A 
HOSIE 2 A 
HOSIE 2 A 
3D 14/15 XL 13 
DUN 54 
DUN 54 
HOSIE 2 B 
HOSIE 2 A 
HOSIE 2 A 
HAR 13 
HOSIE 2 A 



BRITISH AVONIAN CONODONT FAUNAS 



295 



Slide Nos of 


figured 


Name of Conodont 


specimens 




X61 


Cavusgnathus charactus (Rexroad) 


X62 


charactus (Rexroad) 


X63 


convexus Rexroad 


X64 


cristatus Branson & Mehl 


X65 


naviculus (Hinde) 


X66 


naviculus (Hinde) 


X67 


naviculus (Hinde) 


X68 


naviculus (Hinde) 


X 69 


naviculus (Hinde) 


X 70 


? sp. nov. A 


X71 


Clydagnathus cavusformis gen. et. sp. nov. 


X 72 


cavusiformis gen. et. sp. nov. 


X73 


cavusiformis gen. et. sp. nov. 


X74 


cavusiformis gen. et. sp. nov. 


X75 


cavusiformis gen. et. sp. nov. 


X 76 


darensis gen. et. sp. nov. 


X77 


darensis gen. et. sp. nov. 


X 78 


gilwernensis gen. et. sp. nov. 


X79 


unicornis gen. et. sp. nov. 


X80 


unicornis gen. et. sp. nov. 


X8I 


unicornis gen. et. sp. nov. 


X 82 


gen. et. sp. nov. A 


X83 


Euprioniodina caverna (Collinson & Druce) 


X84 


microdentata (Ellison) 


X85 


sp. 


X 86 


sp. nov. A 


X 87 


Gnathodus delicatus Branson & Mehl 


X 88 


simplicatus sp. nov. 


X 89 


simplicatus sp. nov. 


X90 


simplicatus sp. nov. 


X91 


simplicatus sp. nov. 


X92 


Gnathodus ? sp. nov. 


X93 


bilineatus (Roundy) 


X94 


bilineatus (Roundy) 


X95 


commutatus. Branson & Mehl 


X96 


commutatus. Branson & Mehl 


X97 


commutatus. Branson & Mehl 


X98 


cuneiformis. Mehl & Thomas 


X99 


girtyi collinsoni subsp. nov. 


X 100 


girtyi collinsoni subsp. nov. 


X 101 


girtyi collinsoni subsp. nov. 


X 102 


girtyi collinsoni subsp. nov. 


X103 


girtyi girtyi Hass 


X 104 


girtyi girtyi Hass 


XI05 


girtyi girtyi Hass 


X 106 


girtyi girtyi Hass 


X 107 


girtyi simplex Dunn 


X 108 


girtyi simplex Dunn 


X 109 


Ozarkodina cf. elegans (Stauffer) 



Sample Number 

HAR 13 
HAR 13 

3D i4/!5 
3D 22 

HOSIE 2 B 
Gilm 2 

3D I4A5 
3D 14/15 
HOSIE 2 A 
ZLA 32 
KL7 
KL2 
KL5 
KL 5 
KL5 
ZLA 13 
ZLA 27 
KL 1 
ZLA 14 
ZLA 14 
ZLA 11 
KL I3 

3D 14/15 
GILM 2 
K 14 

HOSIE 2 B 
ZLA 6 
Z38 
ZLA 33 
ZLA 33 
ZLA 33 
ZL8 
3 d 14/15 
3D 14/15 
3D 14/15 
3D 14/15 
3D 12 
S 11 

3D 14/15 
3D 14/15 
3D 14/15 
3D 14/15 
HOSIE 2 A 
HOSIE 2 A 
HOSIE 2 A 
HOSIE 2 A 
HOSIE 2 A (1) 
HOSIE 2 A 5 
Z 19 



296 



BRITISH AVONIAN CONODONT FAUNAS 



Slide Nos of 
figured 
specimens 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 



IO 

II 

12 

13 
14 
15 
16 

17 
18 

19 

20 

21 

22 

23 
24 
25 
26 

27 
28 

29 
30 
31 
32 

33 
34 
35 
36 
37 
38 
39 
40 

4i 
42 
43 
44 
45 
46 

47 
48 

49 

50 
5i 
52 
53 
54 
55 
56 
57 
58 
59 



Name of Conodont 

Gnathodus girtyi simplex Dunn 
girtyi simplex Dunn 
girtyi soniae subsp. nov. 
girtyi soniae subsp. nov. 
girtyi soniae subsp. nov. 
girtyi soniae subsp. nov. 
girtyi turritus Collinson & Druce 
girtyi subsp. nov. 
girtyi subsp. nov. 
girtyi subsp. nov. 
homopunctatus Ziegler 
homopunctatus Ziegler 
homopunctatus Ziegler 
homopunctatus Ziegler 
mononodosus sp. nov. 
mononodosus sp. nov. 
mononodosus sp. nov. 
nodosus Bischoff 
nodosus Bischoff 
nodosus Bischoff 
Polygnathus sp. 
Gnathodus punctatus (Cooper) 
punctatus (Cooper) 
punctatus (Cooper) 
symmutatus sp. nov. 
symmutatus sp. nov. 
symmutatus sp. nov. 
symmutatus sp. nov. 
sp. 
Hibbardella (Hibbardella 

(Hibbardella 

(Hibbardella 

(Hibbardella 

(Hibbardella 

(Hibbardella 

(Hibbardella 

(Hibbardella 

(Hibbardella 

(Hibbardella 



Sample Number 



A 
A 



) acuta Murray & Chronic 

) milleri Rexroad 

) milleri Rexroad 

) milleri Rexroad 

) ortha Rexroad 

) parva sp. nov. 

) parva sp. nov. 

) cf. macrodentata Thomas 

) cf . macrodentata Thomas 

) cf. macrodentata Thomas 

(Hassognathus) separata (Branson & Mehl) 

(Hassognathus) separata (Branson & Mehl) 

(Roundya) barnettana Hass 

(Roundya) barnettana Hass 

(Roundya) barnettana Hass 

(Roundya) barnettana Hass 
Pseudopolygnathus vogesi sp. nov. 
Hindeodella antecomplex Collinson & Druce 

antecomplex Collinson & Druce 

cooperi (Elias) 

cooperi (Elias) 



B 



HOSIE 2 
HOSIE 2 
3D 8 
3D 12 
3D 14/15 
3D 14/15 
3D 23 
CYD 7 A 
CYD 7 A 
CYD 7 A 
3D 14/15 
3D 14/15 
3D 14/15 
3D 14/15 
3D 14/15 
3D 14/15 
3D 14/15 
3D 14/15 
3D 14/15 
HOSIE 2 
(SL 461) D 22 
Z38 
Z38 
Z38 
3D 10 
3D 10 
3D 14/15 
3D 14/15 
HOSIE 2 A 
3D 14/15 
HOSIE 2 
HOSIE 2 
HOSIE 2 
HOSIE 2 
3D 14/15 
3D 14/15 
ZLA 32 
ZLA 32 
KL3 
ZLA 6 
ZLA 7 
3D 14/15 
3D 14/15 
HOSIE 3D 23 
HOSIE 2 C 
K 12 
3D 14/15 
3D 17 
3D 14/15 
3D 14/15 



A 
B 

C 

A 



BRITISH AVONIAN CONODONT FAUNAS 



297 



Slide Nos of 


figured 


Name of Conodont 


specimens 




X 160 


corpulenta Branson & Mehl 


X 161 


corpulenta Branson & Mehl 


X 162 


croka Collinson & Druce 


X163 


croka Collinson & Druce 


X 164 


croka Collinson & Druce 


X165 


croka Collinson & Druce 


X 166 


Spathognathodus costatus costatus (E. R. Bra 


X 167 


hibbardi Collinson & Druce 


X 168 


hibbardi Collinson & Druce 


X 169 


hibbardi Collinson & Druce 


X 170 


ibergensis Bischoff 


X 171 


ibergensis Bischoff 


X 172 


ibergensis Bischoff 


XI73 


ibergensis Bischoff 


XI74 


ibergensis Bischoff 


XI75 


montanaensis (Scott) 


X 176 


montanaensis (Scott) 


XI77 


subtilis Ulrich & Bassler 


X 178 


subtilis Ulrich & Bassler 


XI79 


subtilis Ulrich & Bassler 


X 180 


subtilis Ulrich & Bassler 


X 181 


secarata Collinson & Druce 


X 182 


secarata Collinson & Druce 


XI83 


secarata Collinson & Druce 


X 184 


secarata Collinson & Druce 


X 185 


undata Branson & Mehl 


X 186 


sp. nov. 


X 187 


tenuis Clarke 


X 188 


Hindeodus sp. 


X 189 


sp. 


X 190 


sp. 


X 191 


sp. 


X 192 


alatoides (Rexroad & Burton) 


XI93 


alatoides (Rexroad & Burton) 


X 194 


imperfectus (Rexroad) 


XI95 


Kladognathus clarensis Collinson & Druce 


X 196 


clarensis Collinson & Druce 


XI97 


macrodentatus (Higgins) 


X 198 


macrodentatus (Higgins) 


X 199 


macrodentatus (Higgins) 


X 200 


macrodentatus (Higgins) 


X 201 


Ligonodina beata nom. nov. 


X 202 


beata nom. nov. 


X203 


beata nom. nov. 


X 204 


levis Branson & Mehl 


X205 


levis Branson & Mehl 


X 206 


levis Branson & Mehl 


X 207 


levis Branson & Mehl 


X 208 


magnilaterina sp. nov. 


X 209 


magnilaterina sp. nov. 



Sample Number 

KL3 
KL 19 
3D 14/15 
3D 14/15 
GILM5 
3D 14/15 
ZLA6 
3D 14/15 3 
3D 14/15 5 
3D 14/15 6 
3D 14/15 
3D 14/15 
3D 14/15 
HOSIE 2 A 
GILM2 
3 D 12 
3D 12 
ZLA33 
ZLA33 
ZLA33 
ZLA 14 
ZLA 3D 14/15 
ZLA 3D 14/15 
ZLA 3D 14/15 
CYD7 A 
3D 14/15 
3D 14/15 
GILM5 
HOSIE 2 A 
HOSIE 2 A 
HOSIE 2 A 
HOSIE 2 A 
HOSIE 2 B 
HOSIE 2 C 
HOSIE 2 B 
3D 10 
3D 10 
3D 14/15 
3D 14/15 
3D 14/15 
DUN 54 
KL19 
ZLA 12 
ZLA 12 
HOSIE 2 A 
HOSIE 2 A 
HOSIE 2 B 
HOSIE 2 B 
HOSIE 2 C 
HOSIE 2 C 



BRITISH AVONIAN CONODONT FAUNAS 



Slide Nos of 
figured 
specimens 
X210 
X 211 
X212 
X 213 
X 214 
X215 
X 217 
X218 
X 219 
X 220 

X 221 
X 222 

X 223 

X224 
X225 

X 226 
X 227 
X 228 
X 229 

X23I 

X 232 

X233 

X234 
X235 

X236 

X237 
X238 

X 239 
X 240 
X 241 

X242 

X243 

X244 

X245 

X246 

X247 

X248 

X 249 

X250 
X25I 
X252 

X253 
X254 
X255 

X256 

X257 

X258 
X259 

X 260 

X26I 



Name of Conodont 

magnilaterina sp. nov. 
magnilaterina sp. nov. 
osborni sp. nov. 
osborni sp. nov. 
roundyi Hass 
roundyi Hass 
sp. A 
? sp. 
? sp. 
Apatognathus porcatus (Hinde) 
Spathognathodus cyrius (Cooper) 
Lonchodina bolbosa Collinson & Druce 
bolbosa Collinson & Druce 
bolbosa Collinson & Druce 
furnishi Rexroad 
furnishi Rexroad 
furnishi Rexroad 
furnishi Rexroad 
obtunda Collinson & Druce 
paraclarki Hass 
paraclaviger Rexroad 
paraclaviger Rexroad 
transitans Collinson & Druce 
transitans Collinson & Druce 
transitans Collinson & Druce 
Magnilaterella complectens (Clarke) 
complectens (Clarke) 
complectens (Clarke) 
complectens (Clarke) 
clarkei sp. nov. 
spp. 
sp. 
sp. 
Mestognathus beckmanni Bischoff 
bipluti Higgins 
bipluti Higgins 
bipluti Higgins 
bipluti Higgins 
neddensis sp. nov. 
neddensis sp. nov. 
neddensis sp. nov. 
Metalonchodina bidentata (Gunnell) 
bidentata (Gunnell) 
bidentata (Gunnell) 
bidentata (Gunnell) 
Neoprioniodus antespathatus Collinson & Druce 
antespathatus Collinson & Druce 
barbatus (Branson & Mehl) 
barbatus (Branson & Mehl) 
barbatus (Branson & Mehl) 



Sample Numbei 

HOSIE 2 C 
HOSIE 2 C 
3D 14/15 
3D 14/15 
DUN 54 
3D 14/15 
ZLA 32 
ZLA 11 
3D 10 
DUN 58 
KL 16 
3D 14/15 
3D 14/15 
3D 14/15 
HOSIE 2 C 
HOSIE 2 C 
DUN 54 
GILM3 
3D 14/15 
3D 14/15 
3D 14/15 
3D 14/15 
3D 14/15 
3D 14/15 
3D 10 
HOSIE 2 B 
HOSIE 2 B 
HOSIE 2 B 
HOSIE 2 A 
BIL 102 
HOSIE 2 A 
DUN 76 
GILM 2 
SCC 29 
ANS 15 
ANS 15 
CYD 7 A 
CYD 6 A 
CYD 6 A 
CYD 6 A 
CYD 7 A 
3D 14/15 
3D 14/15 
3D 14/15 
BIL 102 
3D 14/15 
3D 14/15 
ZLA 11 
ZLA 11 
ZLA 13 



BRITISH AVONIAN CONODONT FAUNAS 



299 



Slide Nos of 
figured 
specimens 
X 262 
X 263 
X264 
X 265 
X 266 
X 267 
X 268 
X 269 
X 270 

X27I 

X 272 

X273 

X2 74 

X275 

X 276 

X277 

X 278 
X 279 
X 280 

X28I 

X 282 
X 283 

X284 

X 285 
X 286 
X 287 
X 288 

X289 

X 290 

X29I 

X 292 
X 293 
X 294 

X295 

X 296 
X 297 

X298 

X 299 
X 300 

X30I 

X 302 

X303 

X 304 

X305 

X 306 

X307 
X308 

X 309 
X 310 

X3II 



Name of Conodont 

barbatus (Branson & Mehl) 
confluens (Branson & Mehl) 
confluens (Branson & Mehl) 
conjunctus (Gunnell) 
conjunctus (Gunnell) 
conjunctus (Gunnell) 
montanaensis (Scott) 
montanaensis (Scott) 
montanaensis (Scott) 
montanaensis (Scott) 
peracutus (Hinde) 
peracutus (Hinde) 
peracutus (Hinde) 
peracutus (Hinde) 
scitulus (Branson & Mehl) 
scitulus (Branson & Mehl) 
scitulus (Branson & Mehl) 
spathatus Higgins 
tulensis (Pander) 
varians (Branson & Mehl) 

sp. nov. A 
cf. armatus (Hinde) 
cf. camurus Rexroad 
cf. camurus Rexroad 
cf. camurus Rexroad 
cf. camurus Rextoad 
Ozarkodina cf. congesta Stauffer 
curvata Rexroad 
delicatula (Stauffer & Plummer) 
delicatula (Stauffer & Plummer) 
delicatula (Stauffer & Plummer) 
hindei Clarke 
hindei Clarke 
hindei Clarke 
macra Branson & Mehl 
macra Branson & Mehl 
macra Branson & Mehl 
parva (Huddle) 
plana (Huddle) 
plana (Huddle) 
plumula Collinson & Druce 
plumula Collinson & Druce 
macer (Branson & Mehl) 
macer (Branson & Mehl) 
sp. 
sp. 
sp. 
Patrognathus variabilis gen. et. sp. nov. 
variabilis gen. et. sp. nov. 
variabilis gen. et. sp. nov. 



Sample Number 

ZLA 14 

ZLA 14 

ZLA 33 

HOSIE 2 B 

HOSIE 2 B 

HOSIE 2 C 

3D 14/15 

3D 14/15 

3D 14/15 

3D 14/15 

3D 14/15 

3D 14/15 

3D 14/15 

3D 14/15 

HOSIE 2 A 

HOSIE 2 A 

HOSIE 2 B VI 36 

3D 14/15 

DUN 54 

3D 14/15 

3D 17 

ZLA 14 

VEX 1 

VEX 1 

GILM 1 

HOSIE 2 C 

Z37 
GILM 3 

3D 4 

3D 14/15 

ZLA 31 

HOSIE 2 B 

HOSIE 2 A 

GILM 5 

K 4 

K22 

Z 18 

C? 

K3 
Kl 3 

3D 12 
3D 12 

Z35 

Z 3 8 

c? 

K 13 
Z 16 
KL2 
KL2 
KL2 



3°o 



BRITISH AVONIAN CONODONT FAUNAS 



Slide Nos of 

figured 

specimens 

X312 

x 313 

X3M 
X3I5 
X316 

X317 
X 318 

X3I9 

X 320 

X32I 

X 322 

X323 
X324 
X325 

X 326 

X392 
X327 

X328 

X330 
X33I 

x 332 

X333 
X334 
X335 
X336 
X337 
X338 

X339 
X340 

X34I 
X342 
X343 

X344 

X345 
X346 

X347 
X348 

X349 

X350 
X35I 
X352 
X353 
X354 
X355 
X356 
X357 
X358 
X359 

X360 
X36I 



Name of Conodont 

Plectospathodus ? sp. nov. A 
sp. nov. A 
sp. nov. B 
Prioniodina eireica (Collinson & Druce) 

laevipostica (Rexroad & Collinson) 
laevipostica (Rexroad & Collinson) 
Apatognathus sp. 
Hibbardella (Hassognathus) sp. 
Ligonodina tenuis Branson & Mehl 
tenuis Branson & Mehl 
Magnilaterella spp. 
spp. 
Hindeodella undata Branson & Mehl 
Ozarkodina hindei Clarke 
Apatognathus porcatus (Hinde) 
Cavusgnathus unicornis Youngquist & Miller 
Geniculatus sp. 
Ligonodina tulensis (Pander) 
Prioniodina oweni sp. nov. 

prelaevipostica sp. nov. 
prelaevipostica sp. nov. 
prelaevipostica sp. nov. 
prelaevipostica sp. nov. 
prelaevipostica sp. nov. 
prelaevipostica sp. nov. 
slipans (Rexroad) 
stipans (Rexroad) 
stipans (Rexroad) 
stipans (Rexroad) 
subaequalis (Higgins) 
subaequalis (Higgins) 
subaequalis (Higgins) 
subaequalis (Higgins) 
? sp. nov. 
Polygnathus communis communis Branson & Mehl 
communis communis Branson & Mehl 
communis communis Branson & Mehl 
bischoffi sp. nov. 
bischoffi sp. nov. 
bischoffi sp. nov. 
bischoffi sp. nov. 

inornatus inornatus Branson & Mehl 
inornatus inornatus Branson & Mehl 
inornatus inornatus Branson & Mehl 
inornatus rostratus subsp. nov. 
inornatus rostratus subsp. nov. 
inornatus vexatus subsp. nov. 
inornatus vexatus subsp. nov. 
lacinatus asymmetricus subsp. nov. 
lacinatus asymmetricus subsp. nov. 



Sample Number 

ZLA33 

ZLA33 

3D 17 

3D 17 

CYD 7 A 

CYD 7 A 

HOSIE 2A 

DUN 77 

3D 22 

3D 22 

3D 14/15 

3D 14/15 

3D 14/15 (not figured) 

3D 12 (not figured) 

HOSIE 2C (not figured) 

S 49 

DUN 59 

CYD 3 

ZLA 5 

ZLA 11 

ZLA 11 

ZLA 6 

ZLA 33 
ZLA 33 

ZLA 33 
3D 14/15 
3D 14/15 
3D 14/15 
3D 14/15 
3D 14/15 
3D 14/15 
3D 14/15 
3D 14/15 
GILM3 
ZLA 14 
ZLA 14 
ZLA 14 

sec 
sec 
sec 

C 20 
KLM 1 
KLM 1 
KL 19 
KL 19 
KL 19 
KL 19 
KLM 1 
ZLA 33 
ZLA 32 



BRITISH AVONIAN CONODONT FAUNAS 



301 



Slide Nos of 

figured Name of Conodont 
specimens 

X 362 lacinatus asymmetricus subsp. nov. 

X 363 lacinatus asymmetricus subsp. nov. 

X 364 lacinatus circaperipherus subsp. nov. 

X 365 lacinatus circaperipherus subsp. nov. 

X 366 lacinatus circaperipherus subsp. nov. 

X 367 lacinatus circaperipherus subsp. nov. 

X 368 lacinatus lacinatus Huddle 

X 369 lacinatus lacinatus Huddle 

X 370 lacinatus lacinatus Huddle 

X 371 lacinatus prelobatus subsp. nov. 

X 372 lacinatus prelobatus subsp. nov. 

X 373 lacinatus prelobatus subsp. nov. 

X 374 lacinatus prelobatus subsp. nov. 

X 372 lacinatus prelobatus subsp. nov. 

X 375 lobatus inflexus subsp. nov. 

X 376 lobatus lobatus Branson & Mehl 

X 377 lobatus lobatus Branson & Mehl 

X 378 lobatus lobatus Branson & Mehl 
X 379 Spathognathodus plumulus plumulus sp. et. subsp. nov. 

X 380 plumulus plumulus sp. et. subsp. nov. 

X 381 plumulus plumulus sp. et. subsp nov. 

X 382 plumulus nodosus subsp. nov. 

X 383 plumulus nodosus subsp. nov. 

X 384 plumulus shirleyae subsp. nov. 

X 385 plumulus shirleyae subsp. nov. 

X 386 pulcher (Branson & Mehl) 

X 387 cf. robustus (Branson & Mehl) 

X 388 cf. robustus (Branson & Mehl) 

X 389 scitulus (Hinde) 

X 390 scitulus (Hinde) subsp. nov. A 

X 391 scitulus (Hinde) 

X 392 scitulus (Hinde) 

X 393 scitulus (Hinde) 

X 394 tridentatus (E. R. Branson) 

X 395 tridentatus (E. R. Branson) 

X 396 tridentatus (E. R. Branson) 

X 397 tridentatus (E. R. Branson) 

X 398 bischoffi sp. nov. 

X 399 bischoffi sp. nov. 

X 400 bischoffi sp. nov. 

X 401 bischoffi sp. nov. 

X 402 ziegleri sp. nov. 

X 403 ziegleri sp. nov. 

X 404 ziegleri sp. nov. 

X 405 sp. A 

X 406 sp. B 
X 407 Taphrognathus varians Branson & Mehl 

X 408 varians Branson & Mehl 
X 409 Gen nov. A. sp. 
X 410 Gen. nov. B. sp. 



Sample Number 

ZLA32 
ZLA31 
ZLA32 
ZLA32 
ZLA 32 
ZLA 32 
ZLA 31 
ZLA 31 
ZLA 31 
ZLA 32 
ZLA 32 
ZLA 32 
ZLA 32 
ZLA 32 
KLM 1 
KLM 1 
KL 19 
KL 19 
KL7 
KL2 11 
KL2 11 
KL 1 
KLi 
KL2 
KL3 
ZLA 31 
ZLA 10 
ZLA 10 
DUN 78 
DUN 78 
GILM 1 
HOSIE 2 A 
CYD 7 A 
ZLA 14 
ZLA 14 
ZL8 
KL 19 
GUD 3 
GUD 8 
GUD 4 
GUD 5 
GUD 2 
GUD 9 
GUD 10 
KL3 V 
ZLA 5 
HAR20 
HAR 16 
ZLA 6 
ORZ 1 



30-! 



liklllSH AVON1AN CONODONT FAUNAS 



Slide Nos i> 

figured 

specimens 

X 41 1 

X 412 

X 413 

X 4I4 

x 415 

X 416 

X 417 

X4I8 

X4I9 

X 420 

X42I 

X 422 

X 423 

X 424 

X 425 

X 426 

X427 

X 428 

X429 

X 430 

X43I 
X432 

X433 

X 434 
X 435 

X436 

X437 
X438 

X439 
X 440 

X 441 

X442 

X 443 
x 444 
X445 
X 446 

X447 
X 448 
X 449 
X 45° 
X451 
X452 
X453 
X 454 
X455 
X456 

X457 
X458 

X 459 
X 460 



Name of Conodont 



Sample Number 



Gnathodus avonensis sp. now 

antetexanus Rexroad & Scott 
antetexanus Rexroad & Scott 
antetexanus Rexroad & Scott 
simplicatns sp. no v. 
bilineatus (Roundy) 
bilineatus (Roundy) 
commutatus (Branson & Mehl) 
Ozarkodina plana (Huddle) 

compressa Rexroad 
Gnathodus semiglaber Bischoff 
Hibbardella acuta Murray & Chronic 
sp. 
Lonchodina sp. A 
Gnathodus sp. 

delicatus Branson & Mehl 
Plectospathodus ? sp. nov. B 
sp. nov. B 
Prioniodina latericrescens (Branson & Mehl) 
Polygnathus P. communis communis Branson & Mehl 
Magnilaterella clarkei sp. nov. 
clarkei sp. nov. 
Pseudopolygnathus longiposticus Branson & Mehl 
longiposticus Branson & Mehl 
Spathognathodus cf. campbelli Rexroad 

coaptus (Branson & Mehl) 
ziegleri sp. nov. 
Pseudopolygnathus dentilineatus E. R. Branson 
Gnathodus bilineatus bilineatus (Roundy) 
Polygnathus lobatus lobatus Branson & Mehl 
Hibbardella {Hibbardella) sp. 

Pseudopolygnathus cf. longiposticus Branson & Mehl 

cf. longiposticus Branson & Mehl 

longiposticus Branson & Mehl 

longiposticus Branson & Mehl 

Hindeodella sp. 

Magnilaterella ? sp. 

Pseudopolygnathus cf. longiposticus Branson & Mehl 
cf. longiposticus Branson & Mehl 
Spathognathodus cf. campbelli Rexroad 
cf. campbelli Rexroad 
cf. campbelli Rexroad 
coaptus (Branson & Mehl) 
coaptus (Branson & Mehl) 
costatus costatus (E. R. Branson) 
costatus costatus (E. R. Branson) 
costatus sulciferus (Branson & Mehl) 
costatus sulciferus (Branson & Mehl) 
costatus sulciferus (Branson & Mehl) 
crassidentatus (Branson & Mehl) 



Z38 

ZLA32 

ZLA33 

C 4 

ZLA 32 
3D 14/15 
3D 14/15 
3D 14/15 

K 3 

3D 22A 
Z30 

3D 14/15 
ZLA 32 
ZLA 32 
HOSIE 2 
Z 32 

3D 14/15 
3D 14/15 
Z 22 
KLM 1 
BIL 102 
DUN 54 
Z38 
Z38 

3D 14/15 
Z 36 
GUD 7 
Z17 

3D 14/15 
KL 19 
KL 16 
Z 38 
Z38 
Z38 
Z38 
ZLA 33 
ZLA 37 
Z 38 
Z38 

3D 14/15 
3D 14/15 
3D 14/15 
Z38 
Z 36 
ZLA 6 
ZLA 8 
ZLA 6 
ZLA 12 
ZLA 12 
ZLA 15 



BRITISH AVONIAN CONODONT FAUNAS 



303 



Slide Nos of 
figured 
specimens 
X461 
X 462 
X463 
X 464 

X465 
X 466 

X467 

X 468 

X469 
X470 

X47I 
X472 

X473 

X474 

X475 
X476 

X477 
X478 

X479 

X 480 

X48I 
X482 

X483 

X484 

X485 

X486 

X487 

X 488 
X 489 
X 490 
X 491 
X 492 

X493 

X 494 
X495 
X 496 
X497 
X498 
X 499 
X 500 
X 501 

X502 
X503 

X504 

X505 

X 506 

X507 
X508 

X 509 

X5IO 



Name of Conodont 

crassidentatus (Branson & Mehl) 
crassidentatus (Branson & Mehl) 
crassidentatus (Branson & Mehl) 
cristulus Youngquist & Miller 
cristulus Youngquist & Miller 
cristulus Youngquist & Miller 
cristulus Youngquist & Miller 
cristulus Youngquist & Miller 
cf. cyrius (Cooper) 
cf. cyrius (Cooper) 
cf. cyrius (Cooper) 
elongatus (Branson & Mehl) 
elongatus (Branson & Mehl) 
elongatus (Branson & Mehl) 
elongatus (Branson & Mehl) 
plumulus plumulus sp. no v. 
Pseudopolygnathus dentilineatus E. R. Branson 
dentilineatus E. R. Branson 
dentilineatus E. R. Branson 
dentilineatus E. R. Branson 
dentilineatus E. R. Branson 
expansus sp. nov. 
expansus sp. nov. 
multistriatus Mehl & Thomas 
multistrialus Mehl & Thomas 
multistriatus Mehl & Thomas 
multistriatus Mehl & Thomas 
nodomarginatus (E. R. Branson) 
nodomarginatus (E. R. Branson) 
nodomarginatus (E. R. Branson) 
nodomarginatus (E. R. Branson) 
nodomarginatus (E. R. Branson) 
nodomarginatus (E. R. Branson) 
nodomarginatus (E. R. Branson) 
nodomarginatus (E. R. Branson) 
postinodosus sp. nov. 
primus Branson & Mehl 
primus Branson & Mehl 
primus Branson & Mehl 
primus Branson & Mehl 
vogesi sp. nov. 

triangulus cf. pinnatus Voges 
vogesi sp. nov. 
vogesi sp. nov. 
vogesi sp. nov. 
vogesi sp. nov. 
vogesi sp. nov. 
Hibbardella abnormis Branson & Mehl 
Gnathodus nodosus Bischoff 
nodosus Bischoff 



Sample Number 

ZLA 15 
ZLA 15 
ZLA 15 
HOSIE 2 A 
HOSIE 2 A 
HOSIE 2 B 
VEX 1 
GILM 1 
KL 19 
KL 16 
KLM 1 
KL20 
ZLA 6 
ZLA 10 
ZL 8 
KL 4 
Z17 
Z 16 
Z 16 
Z 16 
Z 16 
K 12 
K 12 
ZLA 33 
Z 26 
Z 26 
Z 26 
ZLA 31 
ZLA 31 
ZLA 31 
ZLA 31 
ZLA 32 
ZLA 32 
ZLA 32 
ZLA 32 
Z38 
Z17 
Z17 
Z 22 
Z17 
KL2 

c 7 

K 12 
K 12 
KL 12 
KL2 

KL9 
CYD 6 
3D 14/15 
3^ 14/15 



3°4 

Slide Nos of 
figured 
specimens 
X 511 
X512 
X513 
X5H 
X515 
X516 

X517 
X 518 

X519 
X520 
X 521 

X522 

X523 
X524 
X525 

X526 

X527 

X528 
X529 
X530 
X53I 
X532 
X533 
X534 
X535 
X536 
X537 
X538 
X539 

X540 

X54I 

X542 

X543 

X544 

X545 
X546 

X547 
X548 

X 549 
X550 
X551 
X552 
X553 
X554 
X555 
X556 
X557 
X558 
X559 
X 560 



BRITISH AYONIAN CONODONT FAUNAS 



Name of Conodont 

Magnilaterella sp. 

Spathognathodns pulcher (Branson & Mehl) 
pulcher (Branson & Mehl) 
Hindeodella brevis Branson & Mehl 
Pseudopolygnathus sp. A 
Polygnathus cf. communis Branson & Mehl 
Magnilaterella contraria sp. nov. 
Spathognathodns sp. nov. 
Patrognathus variabilis gen. et. sp. nov. 
Neoprioniodus cf. N. confluens (Branson & Mehl) 
Gnathodns punctatus-Gnathodus semiglaber transition 
Pseudopolygnathus cf. longiposticus Branson & Mehl 
cf. longiposticus Branson & Mehl 
Kladognathus mehli (Rexroad) 

Gnathodus punctatus-Gnathodus semiglaber transition 
Gen. et. sp. indet. 
Lonchodina furnishi Rexroad 
Magnilaterella robusta Rexroad & Collinson 
robusta Rexroad & Collinson 
Polygnathus inornatus rostratus sub. sp. nov. 

sp. 
Scaphignathus ? sp. A 
sp. B 
Siphonodella isosticha (Cooper) 
isosticha (Cooper) 
obsoleta Hass 
sp. A 
sp. 
sp. 
Spathognathodns anteposicornis Scott 
anteposicornis Scott 
anteposicornis Scott 
anteposicornis Scott 
Gnathodus antetexanus Rexroad & Scott 
Pseudopolygnathus cf. longiposticus Branson & Mehl 
primus Branson & Mehl 
longiposticus Branson & Mehl 
Magnilaterella robusta Rexroad & Collinson 
Pseudopolygnathus primus Branson & Mehl 
Apatognathus chauliodus Varker 
Polygnathus inornatus vexatus sub. sp. nov. 
Pseudopolygnathus cf . fusiformis Branson & Mehl 
Magnilaterella contraria sp. nov. 
Spathognatliodus cf. crislulus Youngquist & Miller 
cf. cristulus Youngquist & Miller 
cf. cristulus Youngquist & Miller 
cf. cristulus Youngquist & Miller 
Taphrognathus — Cavusgnathus transition 
Taphrognathus — Cavusgnathus transition 
Taphrognathus — Cavusgnathus transition 



Sample Number 

3D 12 
Z35 
Z35 

3D 14/15 
ZLA 31 
KLM 140 
HOSIE 2 B 
Z 20 
KL 2 
KL 19 
Z38 
Z 38 
Z38 

3D 14/15 
Z 38 
ZLA 31 
3D 23 
DUN 78 
DUN 78 
KL 4 
FAR 4 A 
ZL2 
ZLq 
KL 16 
KL 16 
KLM 1 
KL 16 
K 12 
K 17 
ZLA 15 
ZLA 15 
ZLA 14 
KL IQ 

C 7 
Z38 
Z17 
Z 38 
DUN 78 
Z 18 

HOSIE 2B 
KLM 1 
C 14 
ZLA 33 
ZLA 33 
ZL 18 
ZLA 33 
ZLA 33 
S49 
S 4 9 
S49 



INDEX 



305 



Abergavenny, 18 

Acetic acid, 4 

Africa, North, 64, 65 

Alberta, 9 

Algae, 4, 11, 20 

Algal Series, 30, 51, 275, 277 

America, North, 4, 5, 9, 43-45, 52-57, 59, 

60-65, 77. 97- 106-107, 1 5°. 2 °8. 217. 277 
Anchoralis Subzone, 57, 59, 64-65 
Anchoralis-bilineatus interval, 64 
Angulodus, 66 

demissus, 68 

gravis, 69 

sp. nov. B, 66 

sp. nov. C, 68, 69 

sp. nov. D, 68, 69 

walrathi, 66 
Anstruther, 30, 270 
Anthraconaia modiolaris Zone, 7 
Apatognathus, 6, 35, 42, 48, 62, 69-77, 9° 

bladus, 35, 44, 69, 70, 71 

chauliodus, 71 

geminus, 35, 42, 44, 71, 72 

geminus — Cavusgnathus Assemblage Zone, 
10, 44, 61, 62 

petilus, 42, 72, 73 

porcatus, 73, 74 

scalenus, 35, 42, 74 

cf. libratus, 43, 75, 76 

sp-. 77 

sp. nov. A, 76, 77 

varians, 40, 69, 75 
Arenigian, 5 
Arnsbergian, 18 
Argyll, 30, 244 
Arkansas, 10 
Arkansas Novaculite, 9 
Askeaton, Eire, 61 
Askrigg Block, 26 
Assemblage Zones 

Britain, 35-51 

Germany, 52-63 

U.S.A., 52-63 " 
Auchenmade, 30 

Australia, 11, 32, 53, 58, 60, 65, 178 
Austria, 8 
Avesnois, 9 

Avon Gorge, 5, 6, 13, 17-18, 21, 32, 35-36, 
39-41. 44. 46-4 8 . 5i. 53. 55-58. 60-62, 
65-66, 78, 98, 106, 176, 193, 200, 202, 
204, 205, 217, 244-56, 277 
Avonia bassus, 17 



Avonian, 13-15, 17-18, 55, 57, 61, 65, 158, 

203, 206-207, 216, 228 
Avonian sections, 13, 17-18, 24, 55 
Avonian Zones, 59 

conodont, 35 

coral-brachiopod, 13-17 
Ayrshire, 29, 30, 51, 244, 272-274, 277 
Ayrshire Coalfield, 29 
Aymestry Limestone, 6 

Bactrognathus, 35, 60, 64-65 

communis, 106 
Bactrognathus — Polygnathus communis 

Assemblage Zone, 56, 60 
Bactrognathus — Taphrognathus Assemblage 

Zone, 10, 56, 61 
Barness East, 30, 50, 266 
Barnett Formation, 10 
Belgium, 9, 17, 36, 39-41. 52-54. 62-65 
Berwick Formation, 60 
Bilston Burn, 30, 269 
Birdshill Limestone, 5 
Bishopsteignton, 6 
Bivalves, 13, 20 
Black Lias Quarry, 23 
Black Rock Limestone, 6, 17, 247 
Black Rock Quarry, 21, 25 
Brachiopods, 11, 13, 20, 27 
Broadstone Limestone, 30, 51 
Bollandian, 18 
Bonaparte Gulf, 57-58 
Boulonnais, 9 
Breconshire, 66, 244 
Bristol, 19, 22, 66, 228 
Bryn Pig Limestone, 5 
Bryozoa Bed, 20 

Burlington Formation, 42, 57, 61, 64, 97, 277 
Burrington Combe, 15 
Bushberg — Hannibal, 9, 236 
Bushberg Sandstone, 9, 56 
B2 Zone, 18 

Callington, 6 

Calciferous Sandstone Measures, 4, 29, 30, 50 

Calciferous Sandstone " Series ", 13, 18, 29, 

270, 272 
Caney Formation, 9 
Caninia Oolite, 15, 18, 20, 22, 32, 61 
Caninia Shales, 20 
Caninia Zone, 15, 18, 20, 249, 250 
Caradocian, 5 

Carboniferous, Lower, 7-9, 11, 13, 19, 53, 243 
Carboniferous Limestone Series, 23, 29, 30 



306 



BRITISH AVONIAN CONODONT FAUNAS 



Carlops, 30, 50 
Carmarthenshire, 5 

Catcraig, 30 

Cavusgnathus, 35, 43-44, 62, 77-78, 85, 150, 
180, 219, 236, 242, 245 

alia, 77, 78 

char actus, 35, 43, 79-80, 83 

convexus, 35, 50, 80-81, 83 

cristatus, 43, 51, 80-81 

regularis, 81 

naviculus, 45, 50, 81-82, 84 

unicornis, 35, 43-44, 82-84 

? sp. nov. A, 84 
Cavusgnathus unicornis — Apatognathus 

libratus Zone, 43, 51, 61 
Celloni Zone, 5 
Cementstones, 13 
Cementstone Group, 13, 29 
Centrognathus spurius, 68 
Cephalopod, 7, 9, 65 
Chapel Hill Limestone, 10 
Chapel Point, 30, 266 
Chappel Limestone, 106, 203 
Chester, 10, 45, 63 

Chouteau Formation, 40-41, 55-57, 64, 277 
Chudleigh, 6 

Cladognathus primus, 130 
Clee Hills, 25 

Cleistopora Zone, 15, 20, 246, 261 
Clevedonian, 15 
Cleveland Hills, 7 
Clifton, 21, 22 
Clown Marine Band, 7 

Clydagnathus , 4, 32, 53-54, 63, 84, 178-179, 
219, 230, 236, 245 

cavusformis, 32, 84-86, 88 

darensis, 32, 41, 48, 86-87, 89 

gilwernensis , 32, 36, 38, 48, 86, 87-88 

sp. nov. A, 88-89 

unicornis, 32, 40-41, 48, 88 
Coal Farm, 30, 270 
Coal Measures, 7 
Colsterdale Marine Beds, 7 
Concretionary Beds, 20, 22, 253 
Conodonts, affinities of, 4 

composition of, 4 

function of, 5 
Coral — brachiopod zones, 13-16, 20, 21 
Cornbrook Sandstone, 25 
Costatus Zone, 53 
County Clare, 7 
Cracoean, 18 
Craigmore Ironstone, 7 



Craig-y-Dinas, 23 

Craven Lowlands, 13 

Crinoids, 11, 20-21 

Crtig Limestone, 5 

Ctenognathus murchisoni, 222 

Cu I Stage, 4, 11, 36, 39, 53-55, 65, 200, 203, 

217 
Cu I — Cu II Stages, 236, 277 
Cu II Stage, 4, 9, 11, 39-43. 55-57. 59-62, 

64-65. 150. 236, 277 
Cu III Stage, 4, 44-45, 61-64, 277 
Culm facies, 1 1 
Cumberland, 6 

Ci Subzone, 15, 18, 31, 42, 57, 62, 245, 277 
C2S1 Subzone, 15, 18, 25, 43, 46, 277 
C Zone, 15, 17, 22, 51, 60, 62, 65, 245 

Dairy, 30 

Dark Shale unit, 55 

Derbyshire and Nottinghamshire Coalfield, 7 

Devon, 18 

Devonian, 5-8, 11, 53, 54, 77, 107, 126, 167, 

178, 181, 200, 202, 222, 243 
Devonian — Carboniferous boundary, 6, 54, 

236 
Dibunophyllum Zone, 15-16, 18, 23, 244, 254, 

255. 256 
Dinant Basin, 62 
Dinantian, 9, 15, 17 
Diplodella, no 

Dockra Limestone, 30, 51, 272 
Doliognathus, 35, 64-65 
excavatus, 64 
latus, 65 
Drumbuie House, 30 
Dryburn Foot, 30 

Dunbar, 30, 45-50, 244, 264-266, 277 
Durham, 26 
Di Subzone, 4, 15, 17, 21, 25, 27, 44, 46, 62, 

277 
D2 Subzone, 4, 15, 17, 21, 23, 27, 44-46, 50, 

62-63, 245, 259, 277 
D3 Subzone, 4, 44-45, 50-51, 260, 277 
D Zone, 15, 18, 22-23, 32, 42, 51, 61-62, 78, 

149, 193, 196, 245, 254 

East Germany, 8 
East Ogwell, 6 
Edenbrook Beds, 6 
Edenork, 6 
Eifelian, 6 
Eire, 45 



INDEX 



3°7 



Elictognathus, 35, 53, 54, 64 

coslatus, 63 
Ellisonia, no 
Emsian, 6 

England, South West, 6, 54 
English River Formation, 9, 10 
Eosteinhornensis Zone, 6 
Erdbach Kalk, 8 
Esneux, 53 

Eumorphoceras Zone, 51 
Euprioniodina, 89, 90 

caverna, 90 

deflecta, 89 

microdenta, 91 

sp. nov. A, 91, 92 

sp., 92 
Europe, western, 8 
Ei Stage, 4, 18 
Ejb Stage, 26 
E2 Stage, 4, 18 
E2a Stage, 62 
E Zone, 62 

Fall Bay, 61 

Fammenian, 9, 53-54 

Farlovian, 25 

Farlow, 25, 48, 66, 244, 261, 277 

Farlow Sandstones, 25 

Fern Glen Formation, 9, 42, 60, 64, 97, 277 

Fife, 29, 30, 45, 50, 52, 244, 270-271, 277 

Fife Coalfield, 29 

Fish Bed, 6 

Fitzroy Basin, 178 

Five Yard Limestone, 26-27, 45- 48. 263, 277 

Foraminifera, n, 21, 54 

France, 9, 52, 63, 64-65 

Franco-Belgian Province, 9, 52, 64-65, 178 

Frasnian, 6 

Gastropods, n, 20 

Gattendovfia Zone, 8, 17 

Gayle Beck, 28, 262 

Gayle Limestones, 26-27, 4^ 

Gelli-grin Limestone, 5 

Gen. nov. A. sp., 242-243 

Gen. nov. B. sp., 243 

Geniculatus, 92 

Germany, 4, 7-10, 40, 41, 44-45, 52, 54-57, 

59, 62-65, 208, 243 
Gilmerton Limestone, 30, 50, 267 
Gilwern, 87 
Girvanella Bed, 27 
Givetian, 6 



Glamorgan, Vale of, 22 
Glenconse Burn, 30 
Glen Dean Formation, 10, 45, 63 
Glengarnock, 30, 51, 277 
Glen Park Formation, 55, 217 
Glonbeith Castle, 30 
Gloucestershire, n 
Gnathodids, 34, 41-43 
Gnathodus, 34, 56-58, 93, 245 

antetexanus, 34, 40-42, 48, 56-57, 60, 64, 

93-94, 98 
avonensis, 34, 41, 94 

bilineatus, 34, 44-46, 51, 62-64, 94~95> 99 
bilineatus — Cavusgnathus charactus 

Assemblage Zone, 10, 63 
cf. girtyi, 64 

commutatus, 34, 45, 51, 64, 95-96, 104-105 
cuneiformis, 34, 43, 64, 97, 206 
delicatus, 34, 39-41, 56-57, 64, 97-98, 277 
girtyi, 50-51, 57, 61, 63-64, 99-102, 109 
girtyi collinsoni, 34, 45, 48, 51-52, 63, 

99-100 
girtyi collinsoni Assemblage Zone, 48, 

50-51, 63, 277 
girtyi Form A, 62, 102 
girtyi Form B, 62 
girtyi Form C, 63 

girtyi girtyi, 34, 44, 45, 51, 62, 98, 100-102 
girtyi simplex, 34, 44-45, 51, 62 
girtyi soniae, 101-102 
girtyi turritns, 34, 45, 48, 50-51, 102 
homopunctatus, 34, 44-45, 48, 62-64, io 3> 

108 
kockeli, 53, 55 
kockeli — Pseudopolygnathus dentilineatus 

Zone, 8, 54-55 
mononodosus, 34, 44-45, 48, 50-51, 63, 

103-105 
mononodosus Assemblage Zone, 45, 48, 50, 

63. 277 
mosquensis, 93 

nodosus, 45, 51, 63, 94, 104-105 
punctatus , 34, 60, 105-106 
semiglaber , 34, 40-42, 56-57, 60, 62, 64, 98, 

106-107 
semiglaber — Pseudopolygnathus multi- 

striatus Assemblage Zone, 10, 56, 59-60 
simplicatus, 34, 40-41, 64, 94, 107-108 
symmutatus, 44, 103-104, 108 
? sp. nov., 109 
sp, 109 

sp. n. B — Gnathodus kockeli Assemblage 
Zone, 55 



3 o8 



BRITISH AVONIAN CONODONT FAUNAS 



texanns, 42, 61-62, 206 
Golconda Group, 10 
Goniatites Zone, 13, 18, 26, 52, 54 
Gower, 18, 22, 61, 244 
Gramscatho Limestone, 6 
Grassington, 26 
Grassy Creek, 236 
Great Quarry, 22, 251-252 
Great Scar Limestone, 26 

Hainault, 9 

Hangenberg Limestone, 17 

Hangenberg Schiefer, 8 

Hannibal Formation, 9, 36, 39-40, 53-56, 60, 

200, 217 
Hannibal — Upper Chouteau, 277 
Harden Burn, 30, 51, 275 
Hardraw Scar Limestone, 26-28, 48, 277 
Hartz Mountains, 64 
Hassognathus, 111 
Hastiere Limestone, 17 
Hibbardella, 110-111 
Hibbardella (Hassognathus) 117 
Hibbardella {Hibbardella) abnormis, 44, 

IIO-III 

acuta, 112 

miller i, 113 

ortha, 113-115 

parva, 11 4-1 15 

cf. macrodentata, 115, 117 

separata, 117 

sp., 115-116 

? sp., 117 
Hibbardella (Prioniodus) angulata, 110-111 
Hindeodella, 118 

antecomplex , 35, 118-119 

brevis, 119 

cooperi, 120-123 

corpulenta, 35, 39, 120-121, 243 

croka, 121 

hibbardi, 122 

ibergensis, 123 

montanaensis , 123-124 

secarata, 124 

segaformis, 64-65 

subtilis, 35, 40, 118, 125-126 

tenuis, 126-127 

undata, 35, 127 

sp., 127 

sp. nov., 128 
Hindeodus, 128 

alaloides, 129 

imperfectus, 129, 130 



sp., 130 
Honnetal, 54 
Hosie Limestone, 30, 51, 271, 273 

Lower, 51-52, 271 

Middle, 51-52, 271 

Upper, 271 
Hurlet Limestone, 51-52, 270-271 
Hiiy, 54 

Illinois Basin, 10, 56 

Index Limestone, 30, 51, 274 

Indiana, 10, 59 

Intercontinental correlation, 36 

Intra-Avonian unconformity, 245 

Ireland, 11, 13, 45 

Iowa, 9-10, 63 

Keisley Limestone, 5 

Kentucky, 10 

Keokuk Formation, 9-10, 43, 277 

Kidwellian, 15 

Kilsyth, 6 

Kinderhookian Series, 59, 98 

Kinkaid Formation, 10 

Kladognathus , 35, 130-132 

-Cavusgnathus naviculus Assemblage Zone, 
10 

clarensis, 131 

macro dentatus , 132 

mehli, 132 
K Zone, 4, 15, 17-18, 20-21, 25, 31-33, 36, 
39-40, 46, 48, 52-53, 55-56, 59, 63, 
78, 86, 200-203, 217, 221, 244, 245-246, 
257, 261, 277 
" Lagoon " facies, 11 

Laminosa Dolomites, 16, 20, 22, 31-32, 60-61 
Lancashire, 7 
Landelies Limestone, 17 
Legend for lithological sections, 276 
Leicestershire and South Derbyshire 

Coalfield, 7 
Leigh Woods, 21-22 
Leinster, 11 
Ligonodina, 118, 133, 145 

beata, 35, 39, 48, 133, 139 

clarki, 143 

complectens, 132 

levis, 45, 134, 135 

magnilaterina, 135-136 

osborni, 136-137 

pectinata, 133 

roundyi, 137-138 

tenuis, 138 



INDEX 



309 



lulensis, 139 

sp. A, 139 

sp., 139, 140 

? sp., 139, 140 
Lilleshall, 25 
Limestone III A, 27 

III B, 27 

III C, 27 

IV A, 27 
IV B, 27 

IV C, 26-27 

V A, 26-27 

VI A, 26-27 
VI B, 26-27 

Limestone Coal Group, 18, 29-30 
Linn Limestone, 30 

Lower, 30, 51 

Upper, 30, 51, 274 
Linn Spout, 30, 51 
Little Wenlock, 25 
Llandeilian, 5 
Llandeilo Limestone, 5 
Llandovery, 5 
Llanelli Quarry, 25 
Lodgepole Limestone, 55 
Lonchodina, 140 

bolbosa, 140 

furnishi, 141, 142 

obtunda, 142 

paraclarki, 143 

paraclaviger, 143-144 

transitans, 144 

typicalis, 140 

sp. A, 144 
Long Craig Limestone, Upper, 30, 50, 264 
Louisiana Limestone, 53, 222, 236 
Lower Limestone Group, 4, 18, 29-30, 50-51, 

264-269, 271-273 
Lower Limestone Shale, 6, 13, 17, 36, 54 

Machrihanish, 30 
Macropolygnathns, 201 

ithus, 201 
Magnilaterella, 51, 132, 135, 144-148 

clarkei, 35, 146-147 

complectens , 145-146 

contraria sp. nov., 147-148 

robusta, 144, 148 

sp., 149 

spp., 149 

? sp., 149, 150 
Main Limestone, 26 
Malvern Hills, 5 



Marble Cliff Beds, 6 
Marbre Noir Series, 17 
Maury Shale, 10 
McCraney Limestone, 10 
Mellte Bridge, 23 
Melmerby Scar Limestone, 26 
Menard Formation, 10-11 
Merocanites, 18 

Mestognathus, 35, 51, 57, 61, 78, 150-152, 
180, 219 

beckmanni, 42-45, 61-63, J 5° 

beckmanni — Gnathodus bilineatus Zone, 44, 
63 

bipluti, 35, 44-45, 152-153 

neddensis, 35, 45, 153, 154 
Metalonchodina, 131, 154 

bidenlata, 154-156 
Middle Limestone, 26-27, 4^. 277 
Midland Coalfields, 7 
Midland Valley, Scotland, 4, 13, 29, 66 
Midlothian, 150, 244, 267-269, 277 
Millstone Grit, 7, 22, 26 
Milston Bridge, 30 
Mississippian, 9-10, 55, 200, 217 
Mississippi Valley, 4-5, 10-11, 36, 41, 44-45, 

52-53. 55. 57-63. 77, 217. 277 
Missouri, 9, 56, 59 
Modiola phase, n, 15 
Monmouthshire, 66, 244 
Montana, 9, 11, 55, 179 
Montfort, 53 
Muensteroceras, 18, 60 

inconstans , 18 
Mullion Island, 6 
Mumbles, 23 

Namurian, 4, 7, 18, 45, 62, 177 
Neal Point, 6 
Neoprioniodus, 90, 156 

antespathatus , 156, 157 

cf. armatus, 167 

barbatus, 40, 158 

cf. camurus, 167 

confluens, 158-159 

conjunctus, 159-160 

montanaensis , 44, 160-161 

peracutus, 35, 161-162 

scitulus, 35, 45, 162-163, ID 5 

spathatus, 163-164 

tulensis, 45, 164-165 

varians, 165-166 

sp. nov. A, 166-167 
Newhall House, 30 



3'° 



BRITISH AVONIAN CONODONT FAUNAS 



Now Providence Shale, 56, 59 
Non Calcareous Measures, 27 
North Crop (see South Wales Coalfield) 
North Greens Limestone, 30, 268 
North Scar Gill, 28 
North Staffordshire, 7 
Northumberland, 13, 26 
Northumbrian Trough, 13 

Octoplicata Shale, 17 

Oil Shales, 13 

Oil Shale Group, Lower, 29 

Oklahoma, 9, 56, 59 

Old Red Sandstone, 18 

Ordovician, 5 

Oreton, 25, 244 

Oreton Quarry, 262 

Osage series, 59 

Ostracods, 11, 13, 20 

Ozarkodina, 168, 195 

compressa, 169-170, 173 

curvata, 168-169 

delicatula, 1 70-1 71 

cf. delicatula, 177 

cf. elegans, 177 

hindei, 1 71-173 

macer, 173 

macra, 174 

parva, 174-175 

plana, 175 

plnmula, 175-176 

cf. congesta, 176 

sp., 178 

Palaeogeography — British Carboniferous, 12 
Palate Bed, 20 
Palmatolepis , 53 

glabra subsp. indet., 53, 179 

gracilis, 53 
Paoli Formation, 10 
Paraconodonts, 5 
Passage Group, 29 
Patrognathus, 4, 32, 54, 63, 87, 178, 245 

variabilis, 36, 46, 48, 52, 87, 178, 179 
Patrognathus variabilis — Spathognathodus 

plumulus Assemblage Zone, 36, 48 
Pelecypods, 11 
Pella Formation, 10, 63 
Pembrokeshire, 22, 244 
Pendleian, 18 
Pennsylvanian, 7, 177 
Pentamerus Beds, 5 
Pen-y-garnedd Limestone, 5 



Peracuta Shale, 17 
Pericyclus kochi, 18 

princeps, 9, 65 
Pericyclus Stage, 8 
Phragmodus, 136 
Pierson Formation, 59 
Pilton Beds, 6, 54 
Pittenweem, 30 
Plectospathodus, 18 1 

? sp. A, 181 

sp. B, 181 
Polygnathus, 34, 62, 182, 213, 245 

bischoffi, 35, 42, 61, 184-185 

? claviger, 92 

communis, 34, 40, 48, 60-61, 64 

communis communis, 42, 182, 183, 184 

fusiformis, 201 

inornatus, 35, 39, 46, 48, 63, 185 

inornatus inornatus, 34, 36, 38, 48, 57, 
185-186, 192 

inornatus rostratus, 34, 38, 48, 186-187 

inornatus vexatus, 35, 187, 188 

lacinatus, 35, 41, 46, 51, 60, 62, 185, 188 

lacinatus asymmetricus , 35, 41, 188 

lacinatus circaperipherus , 189 

lacinatus lacinatus, 35, 41—42, 189-191 

lacinatus prelobatus , 190-191 

lacinatus Zone, 41, 57, 59, 277 

lobalus lobatus, 34, 36, 38, 48, 185, 191-192 

lobatus inflexus, 35, 38, 192 

macrus, 211 

nodomarginatus, 55 

orthus, 221 

sp., 192, 193 
Portishead Beds, 17 
Portugal, 8 

Pre-Welden Shale Formation, 56 
Prioniodina, 90, 193-194, 197 

eireica, 194-196 

laevipostica, 35, 195-197 

latericrescens, 196 

oweni, 196-197 

prelaevipostica, 197 

stipans, 45, 198 

subaequalis, 45, 198-199 

subcurvata, 90, 194 

? sp. nov., 199, 200 
Prolecanites discoides, 18 
Prospect Hill Siltstone, 9, 10 
Protocanites, 18, 60 
Pseudobreccias, 22, 27 

Pseudopolygnathus, 32-34, 40, 42, 55, 180, 
200, 204, 207, 213, 226, 236, 239, 245 



INDEX 



3ii 



apetodus, 203-204 

attenuatus, 212 

dentilineatus , 32, 40-41, 54, 63, 65, 203, 

208-209, 212, 215-217 
expansus, 32, 209-210, 217 
foliacens, 203 
cf. fusiformis, 210 
lacinatus, 42, 213 
lanceolatus , 206, 212 
cf. longiposticus, 34, 41-42, 46, 206, 

210-212 
multistriatus , 34, 40-41, 46, 60, 65, 202, 

206, 211-212, 216 
nodomarginatus , 32, 41, 212 
primus, 32, 40-41, 200-204, 2 °°, 2 °9. 2I °. 

212, 214-216 
postinodosus, 32, 40, 213, 214, 239 
striatus, 206, 209, 212 
symmetricus , 55 

triangulus inaequalis , 64-65, 203, 206 
triangulus pinnatus, 60-61, 216 
triangulus subsp. indet, 203 
triangulus triangulus, 60, 203, 206 
sp., 54, 214, 218 
vogesi, 32-33, 36, 38, 46, 54, 202, 210, 

216-217 
vogesi — Clydagnathus Assemblage Zone 

54-55 
Pi Stage, 18, 44-45, 62 
Pic Stage, 26 
P 2 Stage, 18, 62 

Quarry I, 21, 246-247 
Quarry 2, 22, 247-248 
Quarry 3, 22, 249 
Quarry 4, 22 

Rheinisches Schiefergebirge, 18 

Rhenaer Kalk, 63 

Rhenoherzynicum, 8 

River Clydach, 24, 84, 86 

River Mellte, 23 

River Nedd, 23, 153 

River North Esk, 30 

River Sychryd, 23 

Rockford Limestone, 10, 56, 59 

Rossmore Beds, 6 

Roundya, 110-111, 116, 139 

barnettana, 111, 116 

sp., 116-117 
Roxburghshire, 30, 51, 244, 275, 277 
Rib Stage, 26 



Salem Formation, 10, 43, 62 
Sauerland, 64, 203 
Saunton, 6 
Saverton Shale, 53 
Scaliognathus , 35, 64-65 

anchoralis, 8, 9, 64-65 

anchoralis — Gnathodus bilineatus 
' interregnum ", 8 

anchoralis Zone, 64 
Scaphignathus, 53, 84-85, 178, 180, 218, 230 

veliferus, 53, 218 

? sp. A, 218 

? sp. B, 219 
Scotland, 5, 18, 29, 36, 49, 50-52, 62, 66, 244, 

277 
Sedalia Formation, 41, 59, 60, 64, 97, 277 
Seminula Zone, 15-16, 18, 20, 251, 252, 253 
Shale Group, Upper, 29 
Shirehampton Beds, 6, 17 
Shropshire, 5, 6, 25, 32, 66, 244-245, 261, 

262, 277 
Siegenian, 6 
Silurian, 5, 6, 181 
Siphognathus duplicatus, 219 
Siphonodella, 32, 36, 46, 53, 55, 57-59, 64, 
185, 219, 222, 236, 245 

cooper i, 106 

crenulata Zone, 8, 55, 60, 64 

duplicata, 63-64 

isosticha, 38-39, 55, 57, 220-221 

isosticha — 5. cooperi Assemblage Zone, 10, 

5&-57. 59 
lobata, 63 

obsoleta, 63-64, 220-221 
— Polygnathus inornatus Assemblage Zone, 

38, 55. 57 
— Pseudopolygnathus triangulus inaequalis 

Zone, 8 
— Pseudopolygnathus triangulus triangulus 

Zone, 8, 55 
quadruplicata, 63 
— quadruplicata — 5. crenulata Assemblage 

Zone, 55-56 
sexplicata, 63 
sp. A, 221 
sp., 221 
Subzone, 4, 55 
sulcata, 54, 55 

sulcata Assemblage Zone, 54 
triangulus triangulus Zone, 55 
zones of Mississippi Valley, 59 
Simonstone Limestone, 26-27, 45> 4^. 

262-263, 2 77 



3»= 



BRITISH AVONIAN CONODONT FAUNAS 



Skateraw, Lower, 30, 50, 265 
Middle, 30, 50 
Upper, 30, 265 
Skipsey's Marine Band, 7 
Snaizeholme Valley, 28, 263 
Somerset, 6, 1 1 
South Dakota, 1 1 
South Staffordshire, 6 
Southern Uplands, 1 1 

South Wales Coalfield, North Crop, 22-24, 

32-33, 35-36, 39, 40-41, 44-48, 50-51, 

54. 5 6 . 58, 63, 66, 95, 102, 193, 200, 

244-245, 257-60, 277 

South West Province, 4, 6, 11, 13, 48, 56, 62, 

244-245, 277 
Spain, 64-65 

Spathognathodus, 33-34, 200, 209, 221-245 
aculeatus, 53-54, 200, 230, 236-237 
anleposicornis, 34, 39, 200, 222-223, 2 3 I > 

236-237 
bidentatus, 107 
bischoffi, 204, 223, 236, 239 
cf. campbelli, 34, 233 
cf. cristulus, 34, 39, 40-42, 48, 233-234 
cf. robustus, 34, 39, 48, 235, 240 
chouteanensis, 229, 231, 235 
coaptus, 224, 225 
costatus, 53-54, 59, 202, 236 
costalus costatus, 33-34, 39-41, 46, 48, 202, 

204, 225-226, 236-237 
costatus costatus — Gnathodus delicatus 

Assemblage Zone, 39, 40, 48, 56-57, 277 
costatus (spinulicostatus) ultimus, 202, 236 
costatus sulciferus, 33-34, 39, 40-41, 200, 

226, 236 
costatus sulciferus — Gnathodus delicatus 

Assemblage Zone, 56 
costatus Zone, 53, 55, 59 
crassidentatus, 33-34, 39, 41, 48, 225-227, 

229, 231, 235, 240 
cristulus, 34, 43, 45, 107, 227, 234 
cyrius, 33-34, 39, 227, 234 
denticulatus , 225, 229 
elongatus, 33-34, 39, 48, 228-229, 231 
plumulus, 34, 54, 79, 230-231 
plumulus plumulus, 33, 36, 39, 46, 53, 85, 

200, 229, 230-231, 236 
plumulus nodosus, 33, 38, 230 
plumulus shirleyae, 33, 36, 230-231 
pulcher, 34, 41, 231 
regularis, 234 
robustus, 46, 235 



robustus — S. tridentatus Assemblage Zone, 

39, 48, 55- 277 

scitulus, 34, 44, 232 

scitulus subsp. A, 232 

sp. A, 239, 240 

sp. B, 240 

spinulicostatus , 202, 230, 236 

spinulicostatus ultimus, 202 

sp. nov., 240, 241 

stabilis, 231 

sulciferus, 230, 235 

tridentatus, 33-34, 39, 41, 48, 206, 230, 
2 3i> 235, 236-237 

ziegleri sp. nov., 236, 238, 239 
Spores, 54 

Staurognathus , 35, 64-65 
St. Genevieve Formation, 10, 44, 63 
St. George's Land, 1 1 
St. Louis Limestone, 10, 63 
St. Louis Formation, 43, 44, 62, 77, 277 
St. Mellion, 6 
Sublaevis Beds, 17 
S2 Subzone, 15, 20, 22, 25, 42-44, 46, 62, 245, 

258, 277 
S Zone, 15, 17, 22, 32, 42-43, 61-62, 245, 251 
Summary, 52 
Synprioniodina, 90 

Tamar Valley, 6 

Tanhouse Beds, 18 

Taphrognathus, 35, 43, 62-63, 7$. 85, 178, 
241-242, 245 
varians, 35, 43-44, 51, 62, 241-242 
varians — Apatognathus Assemblage Zone, 

10, 61-62 
varians — Cavusgnathus — Apatognathus 
Zone, 43, 61 

Teesdale, 26 

Tennessee, 10 

Texas, 203 

Thorny Force Sandstone, 27 

Three Cliffs Bay, 18 

Three Yard Limestone, 26, 28, 45 

Titterstone Clee Hill, 25 

Tm Stage, 53 

Tn la Stage, 53, 63 

Tnn,/Tn2b Stages, 178 

Tn 2 b Stage, 36, 63 

Tn 2c Stage, 36, 39-40. 63 

Tn 3a Stage, 40, 63-65 

Tn 3 b Stage, 9, 41, 42, 64-65 

Tn 3c Stage, 9, 42, 45 

Tonge's Marine Band, 7 



INDEX 



3i3 



Top Hosie Shale, 6 

Torquay, 6 

Tournaisian, 6, 9, 15, 17, 52, 54, 63, 65, 126, 

178 
Tournaisian — Visean boundary, 17, 65 
Trichognathus separatus, 1 1 1 
Trichonodella, no, 130 

imperfecta, 128 
Tyrone, 6 

Unconformity, 64, 245, 277 

Underset Limestone, 26, 28, 45, 263 

United States, 60, 65, 243 

Upper Limestone Group, 4, 18, 29, 30, 51, 

274 
Usk, 6 

Valmeyeran Series, 45, 62, 78, 98 
Vaughan's coral — brachiopod zones, 13-15, 

17. 245 
Vexhim Limestone, 30, 50 
VI Zone, 54 
Virginia, 10 

Visean, 9, 15, 17-18, 45, 52, 63, 77, 126, 177 
Viverdon Down, 6 

Wales, 5, 11 

Warsaw Formation, 10, 43, 62 

Wassonville Dolomite, 10 

Waterlip Quarry, 6 

Welsh Borderland, 6 

Wenlock Limestone, 6 

Wensleydale, 26, 28 

Western Australia, Canning Basin of, 53 



Western Europe, 43, 52, 54-55, 60-62 
West Germany, 15, 36, 39, 52-53, 55, 61, 

200, 217 
Westmorland, 5 
Westphalian, 25 
West Virginia, 10 
Wilsoni Shales, 5 
Windsor Hill, 6 

Windy Gap Formation, 54, 179 
Whitcliffe Flags, 6 
Whitcliffian Limestone, 6 
White River, 59 
Wocklumeria, 8 
Wocklumeria Stage, 54, 202 
Wocklumeria — VI Zone, 54 
Woolhope Inlier, 5, 6 
Wyoming, 11, 54-55, 179 



Yate, 18 

Yoredale Formation, 6, 25, 27-28, 45, 

244, 262-263, 2 77 
Yorkshire, 5, 6, 25, 102, 244, 277 



\, 62, 



Zaphrentis Zone, 15, 16, 247, 262 

Zi Subzone, 15, 21, 60, 64, 203-205 

Z2 Fish Bed, 65 

Z2 Limestone, 22 

Z2 Subzone, 15, 57, 60, 62, 64, 98, 106, 

205-206, 277 
Z Zone, 17, 18, 20, 22, 31-33, 39-40, 42, 46, 

48, 52. 55-56, 60, 65, 78-79, 158, 176, 

200, 202, 209, 216, 244-245, 247, 248, 

258, 262, 277 



PLATES 



PLATE i 
All specimens coated and magnified X 31.5 

Figs, i, 2, 5, 6. Spathognathodus plumulus plumulus sp. nov. 

ia. Outer lateral view of holotype X 476. ib. Oral view of holotype X 476. ic. Aboral 
view of holotype X 476. 2a. Outer lateral view of paratype X 379. 2b. Oral view of paratype 
X 379. 2c. Aboral view of paratype X 379. 5. Outer lateral view of paratype X 380, 
posterior portion missing. 6. Outer lateral view of juvenile paratype X 381, anterior aboral 
portion of blade missing. 

Figs. 3,4. Spathognathodus plumulus nodosus subsp. nov. 

3a. Outer lateral view of paratype X 383, posterior portion missing. 3b. Oral view of paratype 
X 383- 3c. Aboral view of paratype X 383. 4a. Outer lateral view of holotype X 382, 
posterior portion missing. 4b. Oral view of holotype X 382. 4c. Aboral view of holotype 
X 382. 

Figs. 7, 8. Spathognathodus plumulus shirleyae sp. et subsp. nov. 

7a. Outer lateral view of paratype X 385, posterior portion missing. 7b. Oral view of paratype 
X 385. 8a. Outer lateral view of holotype X 384. 8b. Oral view of holotype X 384. 8c. 
Aboral view of holotype X 384. 

Figs. 9-13. Clydagnathus cavusformis gen. et sp. nov. 

9. Oral view of paratype X 72. 10. Oral view of paratype X 73. 11a. Outer lateral view of 
holotype X 75. 11b. Inner lateral view of holotype X 75. 11c. Oral view of holotype X 75. 
1 id. Aboral view of holotype X 75. 12a. Outer lateral view of paratype X 71. 12b. Inner 
lateral view of paratype X 71. 12c. Oral view of paratype X 71. i2d. Aboral view of para- 
type X 71. 13a. Outer lateral view of paratype X 74, posterior portion missing. 13b. Inner 
lateral view of paratype X 74. 13c. Oral view of paratype X 74. 13d. Aboral view of 
paratype X 74. 



Bull. Br. Mus. nal. Hist. (Geol. Suppl.) 5 



PLATE 1 




PLATE 2 
All specimens coated and magnified x 31.5 



Fig. 1. Clydagnathus gilwernensis gen. et sp. nov. 

a. Oral view of holotype X 78. b. Outer lateral view of holotype X 78. 
view of holotype X 78. d. Aboral view of holotype X 78. 



c. Inner lateral 



Figs. 2, 3, 5. Clydagnathus unicornis gen. et sp. nov. 

2a. Oral view of holotype X 79. 2b. Outer lateral view of holotype X 79. 2c. Inner lateral 
view of holotype X 79. 2d. Aboral view of holotype X 79. 3a. Oral view of paratype X 80. 
3b. Outer lateral view of paratype X 80. 3c. Inner lateral view of paratype X 80. 3d. Aboral 
view of paratype X 80. 5a. Oral view of paratype X 81. 5b. Inner lateral view of paratype 
X 81. 

Fig. 4. Clydagnathus gen. et sp. nov. A 

a. Oral view of specimen X 82. b. Outer lateral view of specimen X 82. c. Inner lateral 
view of specimen X 82. d. Aboral view of specimen X 82. 

Figs. 6, 7. Clydagnathus darensis gen. et sp. nov. 

6a. Oral view of holotype X 77. 6b. Outer lateral view of holotype X 77. 6c. Inner lateral 
view of holotype X 77. 6d. Aboral view of holotype X 77. 7a. Oral view of paratype X 76. 
7b. Outer lateral view of paratype X 76. 7c. Inner lateral view of paratype X 76. 7d. Aboral 
view of paratype X 76. 

Figs. 8-1 i. Patrognathus variabilis gen. et sp. nov. 

8a. Oral view of paratype X 310. 8b. Lateral view of paratype X 310. 9a. Oral view of 
paratype X 519. 9b. Aboral view of paratype X 519. 9c. Lateral view of paratype X 519. 
10a. Oral view of paratype X 309. 10b. Aboral view of paratype X 309. ioc, Lateral view 
of paratype X 309. 11 a. Oral view of holotype X 311. 11b. Aboral view of holotype X 311. 
iic. Lateral view of holotype X 311. 

Fig. 12. Scaphignathus ? sp. B 

a. Oral view of specimen X 533. b. Inner lateral view of specimen X 533. c. Aboral view 
of specimen X 533. 



Fig. 13. Scaphignathus ? sp. A 

a. Oral view of specimen X 532. b. Inner lateral view of specimen X 532. c Aboral view 
of specimen X 532. 



Bull. Br. Mus. nat. Hist. (Geol. Suppl.) 5 



PLATE 2 




PLATE 3 
All specimens coated and magnified X 31.5 

Figs. 1-4. Spathognathodus crassidentatus (Branson & Mehl) 

ia. Inner lateral view of specimen X 463. ib. Aboral view of specimen X 463. 2a. Inner 
lateral view of specimen X 460. 2b. Oral view of specimen X 460. 3a. Inner lateral view of 
specimen X 461. 3b. Aboral view of specimen X 461. 4a. Inner lateral view of specimen 
X 462. 4b. Aboral view of specimen X 462. 

Figs. 5-8. Spathognathodus anteposicornis Scott 

5a. Inner lateral view of specimen X 540. 5b. Oral view of specimen X 540. 6a. Inner 
lateral view of specimen X 543. 6b. Aboral view of specimen X 543. 7a. Inner lateral view 
of specimen X 541. 7b. Aboral view of specimen X 541. 8a. Inner lateral view of specimen 
X 542. 8b. Oral view of specimen X 542. 

Figs. 9-12. Spathognathodus tridentatus (E. R. Branson) 

9a. Inner lateral view of specimen X 395. 9b. Oral view of specimen X 395. 9c. Aboral view 
of specimen X 395. 10a. Inner lateral view of specimen X 396. 10b. Oral view of specimen 
X 396. ioc. Aboral view of specimen X 396. 11a. Inner lateral view of specimen X 397. 
11b. Oral view of specimen X 397. 11c. Aboral view of specimen X 397. 12a. Inner lateral 
view of specimen X 394. 12b. Oral view of specimen X 394. 12c. Aboral view of specimen 
X 394- 

Figs. 13-15. Spathognathodus costatus costatus (E. R. Branson) 

13a. Inner lateral view of specimen X 456. 13b. Aboral view of specimen X 456. 14a. Inner 
lateral view of specimen X 166. 14b. Oral view of specimen X 166. 15a. Inner lateral view 
of specimen X 455. 15b. Oral view of specimen X 455. 

Figs. 16-18. Spathognathodus costatus sulciferus (Branson & Mehl) 

16a. Inner lateral view of specimen X 459. 16b. Oral view of specimen X 459. 17a. Inner 
lateral view of specimen X 458. 17b. Aboral view of specimen X 458. 17c. Oral view of 
specimen X458. 18a. Aboral view of specimen X 457. 18b. Inner lateral view of specimen 
X 457. 18c. Oral view of specimen X 457. 



Bull. Br. Mus. nat. Hist. (Geol. Suppl.) 5 



PLATE 3 



J^^^k i^HWrfil il ^ ^JMl A i fcHtmrirff i^ l l 

la 2a 3 a 4a 



2b 3b 4b 

mm* **4k tfntui *ma 

5a 6a 7a "^ 8a 



11a 12a 






♦ «»• 



PLATE 4 
All specimens coated and magnified X 31.5 

Figs. 1-4. Spathognathodus bischoffi sp. nov. 

ia. Oral view of paratype X 399. ib. Aboral view of paratype X 399. ic. Outer lateral view 
of paratype X 399. id. Inner lateral view of paratype X 399. 2a. Oral view of paratype 
X 400. 2b. Aboral view of paratype X 400. 2c. Outer lateral view of paratype X 400. 
2d. Inner lateral view of paratype X 400. 3a. Oral view of paratype X 398. 3b. Aboral 
view of paratype X 398. 3c. Outer lateral view of paratype X 398. 3d. Inner lateral view of 
paratype X 398. 4a. Oral view of holotype X 401. 4b. Aboral view of holotype X 401. 
4c. Outer lateral view of holotype X 401. 4d. Inner lateral view of holotype X 401. 

Figs. 5-8. Spathognathodus ziegleri sp. nov. 

5a. Oral view of paratype X 437. 5b. Aboral view of paratype X 437. 5c. Outer lateral 
view of paratype X 437. 5d. Inner lateral view of paratype X 437. 6a. Oral view of paratype 
X 402. 6b. Aboral view of paratype X 402. 6c. Outer lateral view of paratype X 402. 
6d. Inner lateral view of paratype X 402. 7a. Oral view of paratype X 404. 7b. Aboral 
view of paratype X 404. 7c. Outer lateral view of paratype X 404. 7d. Inner lateral view 
of paratype X 404. 8a. Oral view of holotype X 403. 8b. Aboral view of holotype X 403. 
8c. Outer lateral view of holotype X 403. 8d. Inner lateral view of holotype X 403. 

Figs. 9-1 1. Spathognathodus pulcher Branson & Mehl 

9a. Oral view of specimen X 386. 9b. Aboral view of specimen X 386. 9c. Lateral view of 
specimen X 386. 10a. Oral view of specimen X 513. 10b. Aboral view of specimen X 513. 
ioc. Lateral view of specimen X 513. 10c. Lateral view of specimen X 513. 11a. Oral 
view of specimen X 512. lib. Aboral view of specimen X 512. 11c. Lateral view of specimen 
X512. 

Fig. 12. Spathognathodus sp. A 

a. Oral view of specimen X 405. b. Aboral view of specimen X 405. c. Lateral view of 
specimen X 405. 



Bull. Br. Mus. nat. Hist. (Geol. Suppl.) 5 



PLATE 4 




PLATE 5 
All specimens coated and magnified X 31.5 

Figs, i, 3, 5-8. Pseudopolygnathus vogesi sp. nov. 

ia. Aboral view of holotype X 155. ib. Oral view of holotype X 155. ic. Lateral view of 
holotype X 155. 3a. Aboral view of paratype X 504. 3b. Oral view of paratype X 504. 
3c. Lateral view of paratype X 504. 5a. Oral view of paratype X 507. 5b. Aboral view 
of paratype X 507. 5c. Lateral view of paratype X 507. 6a. Oral view of paratype X 505. 
transitional to Ps. expansus. 6b. Aboral view of paratype X 505. 6c. Lateral view of paratype 
X 505. 7a. Aboral view of paratype X 501. 7b. Oral view of paratype X 501. 8a. Aboral 
view of paratype X 506. 8b. Oral view of paratype X 506. 

Figs. 2, 4. Pseudopolygnathus expansus sp. nov. 

2a. Aboral view of paratype X 482. 2b. Oral view of paratype X 482. 2c. Lateral view of 
paratype X 482. 4a. Oral view of holotype X 483. 4b. Aboral view of holotype X 483. 
4c. Lateral view of holotype X 483. 

Figs. 9-13. Pseudopolygnathus dentilineatus E. R. Branson 

9a. Aboral view of juvenile specimen X 478. 9b. Oral view of juvenile specimen X 478. 
9c. Lateral view of juvenile specimen X 478. 10a. Aboral view of juvenile specimen X 477. 
10b. Oral view of juvenile specimen X 477. 10c. Lateral view of juvenile specimen X 477. 
11a. Oral view of specimen transitional from Spathognathodus X 479. 11b. Aboral view of 
specimen transitional from Spathognathodus X 479. 11c. Lateral view of specimen transitional 
from Spathognathodus X 479. 12a. Aboral view of specimen X 480. 12b. Oral view of 
specimen X 480. 12c. Lateral view of specimen X 480. 13a. Aboral view of adult specimen 
X 481. 13b. Oral view of adult specimen X 481. 13c. Lateral view of adult specimen 
X481. 

Figs. 14-16. Pseudopolygnathus multistriatus Mehl & Thomas 

14a. Oral view of specimen X 486. 14b. Aboral view of specimen X 486. 14c. Lateral view 
of specimen X 486. 15a. Aboral view of specimen X 487. 15b. Oral view of specimen X 487. 
15c. Lateral view of specimen X 487. 16a. Oral view of specimen X 485. 16b. Aboral view 
of specimen X 485. 16c. Lateral view of specimen X 485. 



Bull. Br. Mus. nat. Hist. (Geol. Suppl.) 5 



PLATE 5 




PLATE 6 
All specimens coated and magnified X 31.5 

Fig. 1. Pseudopolygnathus cf. fusiformis Branson & Mehl 
a. Aboral view of specimen X 552. b. Oral view of specimen X 552. 

Fig. 2. Pseudopolygnathus multistriatus Mehl & Thomas 

a. Oral view of specimen X 484. b. Aboral view of specimen X 484. c. Lateral view of 
specimen X 484. 

Fig. 3. Pseudopolygnathus sp. A. 

a. Oral view of specimen X 515. b. Aboral view of specimen X 515. c. Lateral view of 
specimen X 515. 

Figs. 4, 5, 7, 10-12. Pseudopolygnathus primus Branson & Mehl 

4a. Aboral view of specimen X 546. 4b. Oral view of specimen X 546. 4c. Lateral view of 
specimen X 546. 5a. Aboral view of specimen X 497. 5b. Oral view of specimen X 497. 
7a. Aboral view of specimen X 499. 7b. Oral view of specimen X 499. 7c. Lateral view of 
specimen X 499. 10a. Aboral view of specimen X 500. 10b. Oral view of specimen X 500. 
ioc. Lateral view of specimen X 500. 11a. Aboral view of specimen X 549. 11b. Oral view 
of specimen X 549. uc. Lateral view of specimen X 549. 12a. Aboral view of specimen 
X 498. 12b. Oral view of specimen X 498. 12c. Lateral view of specimen X 498. 

Fig. 6. Pseudopolygnathus postinodosus sp. nov. 

a. Aboral view of holotype X 496. b. Oral view of holotype X 496. c. Lateral view of 
holotype X 496. 

Fig. 8. Pseudopolygnathus dentilineatus E. R. Branson 

a. Aboral view of specimen X 438. b. Oral view of specimen X 438. c. Lateral view of 
specimen X 438. 

Fig. 9. Spathognathodus sp. nov. 

a. Oral view of specimen X 518. b. Aboral view of specimen X 518. c. Lateral view of 
specimen X 518. 



Bull. Br. Mus. nat. Hist. (Geol. Suppl.) 5 



PLATE 6 




TLATE 7 
All specimens coated and mangified X 31.5 

Figs. 1-5. Spathognathodus elongatus (Branson & Mehl) 

ia. Lateral view of specimen X 472. ib. Oral view of specimen X 472. 2. Lateral view of 
specimen X 474. 3. Aboral view of specimen X 472. 4a. Lateral view of specimen X 473. 
4b. Aboral view of specimen X 473. 5a. Lateral view of specimen X 475. 5b. Aboral view 
of specimen X 475. 

Figs. 6, 7. Spathognathodus cf. robustus (Branson & Mehl) 

6a. Lateral view of specimen X 388. 6b. Oral view of specimen X 388. 6c. Aboral view of 
specimen X 388. 7a. Lateral view of specimen X 387. 7b. Oral view of specimen X 387. 
7c. Aboral view of specimen X 387. 

Fig. 8. Spathognathodus sp. B 

a. Lateral view of specimen X 406. b. Oral view of specimen X 406. c. Aboral view of 
specimen X 406. 

Figs. 9-1 i. Spathognathodus coaptus (Branson & Mehl) 

9a. Lateral view of specimen X 454. 9b. Aboral view of specimen X 454. 9c. Oral view of 
specimen X 454. 10a. Lateral view of specimen X 453. 10b. Aboral view of specimen X 453. 
toe. Oral view of specimen X 453. 11a. Lateral view of specimen X 436. lib. Aboral view 
of specimen X 436. 11c. Oral view of specimen X 436. 

Figs. 12-14. Spathognathodus cf. cyrius (Cooper) 

12a. Lateral view of specimen X 471. 12b. Oral view of specimen X 471. 12c. Aboral view 
of specimen X 471. 13a. Lateral view of specimen X 470. 13b. Oral view of specimen 
X 470. 13c. Aboral view of specimen X 470. 14a. Lateral view of specimen X 469. 14b. 
Oral view of specimen X 469. 14c. Aboral view of specimen X 469. 



Bull. Br. Mus. nat. Hist. (Geol. Suppl.) 5 



PLATE 7 



■"'■'"Hirf* rfT'imflfa wawafarift 

1 n A ~ 



5b 



<$&tifk tfUlMfll 4ggj|jiA 



PLATE 8 
All specimens coated and magnified x 31.5 

Figs. 1-4. Spathognathodus cf. campbelli Rexroad 

ia. Lateral view of specimen X 451. ib. Aboral view of specimen X 451. ic. Oral view of 
specimen X 451. 2a. Lateral view of specimen X 435. 2b. Aboral view of specimen X 435. 
2c. Oral view of specimen X 435. 3a. Lateral view of specimen X 452. 3b. Oral view of 
specimen X 452. 3c. Aboral view of specimen X 452. 4a. Lateral view of specimen X 450. 
4b. Oral view of specimen X 450. 4c. Aboral view of specimen X 450. 

Fig. 5. Gnathodus simplicatus sp. nov. 

a. Lateral view of paratype X 88. b. Oral view of paratype X 88. c. Aboral view of 
paratype X 88. 

Fig. 6. Gnathodus cuneiformis Mehl and Thomas 

a. Lateral view of specimen X 98. b. Oral view of specimen X 98. c. Aboral view of 
specimen X 98. 

Figs. 7, 8, 12, 13. Spathognathodus cf. cristulus Youngquist & Miller 

7a. Lateral view of specimen X 554. 7b. Oral view of specimen X 554. 7c. Aboral view of 
specimen X 554. 8a. Lateral view of specimen X 555. 8b. Oral view of specimen X 555. 
8c. Aboral view of specimen X 555. 12a. Lateral view of specimen X 556. 12b. Oral view 
of specimen X 556. 31a. Lateral view of specimen X 557. 13b. Oral view of specimen X 557. 

Figs. 9-1 i. Spathognathodus scitulus (Hinde) 

9a. Lateral view of specimen X 391. 9b. Lateral view of specimen X 391. 9c. Oral view of 
specimen X 391. gd. Aboral view of specimen X 391. 10a. Lateral view of specimen X 392. 
10b. Lateral view of specimen X 392. 10c. Oral view of specimen X 392. iod. Aboral view 
of specimen X 392. 11a. Lateral view of specimen X 393. 11b. Lateral view of specimen 
X 393. iic. Oral view of specimen X 393. nd. Aboral view of specimen X 393. 

Figs. 14-18. Spathognathodus cristulus Youngquist & Miller 

14a. Lateral view of specimen X 466. 14b. Lateral view of specimen X 466. 15a. Lateral 
view of specimen X 467. 15b. Lateral view of specimen X 467. 15c. Oral view of specimen 
X 467. i5d. Aboral view of specimen X 467. 16a. Lateral view of specimen X 468. 16b. 
Lateral view of specimen X 468. 16c. Oral view of specimen X 468. i6d. Aboral view of 
specimen X 468. 17a. Lateral view of specimen X 464. 17b. Lateral view of specimen X 464. 
17c. Oral view of specimen X 464. I7d. Aboral view of specimen X 464. 18a. Lateral view 
of specimen X 465. 18b. Lateral view of specimen X 465. 18c. Oral view of specimen 
X 465. i8d. Aboral view of specimen X 465. 



Bull. Br. Mus. nat. Hist. (Geol. Suppl.) 5 



PLATE 8 



PLATE 9 
All specimens coated and magnified X 31.5 

Figs. 1-4. Pseudopolygnathus nodomarginatus (E. R. Branson) 

ia. Oral view of specimen X 491. ib. Aboral view of specimen X 491. ic. Lateral view of 
specimen X 491. 2a. Oral view of specimen X 489. 2b. Aboral view of specimen X 489. 
3c. Lateral view of specimen X 489. 3a. Oral view of specimen X 490. 3b. Aboral view of 
specimen X 490. 3c. Lateral view of specimen X 490. 4a. Oral view of specimen X 488. 
4b. Aboral view of specimen X 488. 4c. Lateral view of specimen X 488. 

Figs. 5-8. Polygnathus lobatus lobatus Branson & Mehl 

5a. Oral view of specimen X 378. 5b. Aboral view of specimen X 378. 5c. Lateral view of 
specimen X 378. 6a. Oral view of specimen X 376. 6b. Aboral view of specimen X 376. 
6c. Lateral view of specimen X 376. 7a. Oral view of specimen X 377. 7b. Aboral view of 
specimen X 377. 7c. Lateral view of specimen X 377. 8a. Oral view of specimen X 440. 
8b. Aboral view of specimen X 440. 8c. Lateral view of specimen X 440. 

Fig. 9. Polygnathus lobatus inflexus subsp. nov. 

a. Oral view of holotype X 375. b. Aboral view of holotype X 375. c. Lateral view of 
holotype X 375. 

Fig. 10. Cavusgnathus ? sp. nov. A. 

a. Oral view of specimen X 70. b. Aboral view of specimen X 70. c. Inner lateral view of 
specimen X 70. d. Outer lateral view of specimen X 70. 



Bull. Br. Mus. nat. Hist. (Geol. Suppl.) 5 



PLATE 9 




PLATE 10 
All specimens coated and magnified x 31.5 

Figs. 1-3. Polygnathus inornatus vexatus sub. sp. nov. 

ia. Oral view of holotype X 358. ib. Aboral view of holotype X 358. ic. Lateral view of 

holotype X 358. 2a. Aboral view of paratype X 359. 2b. Oral view of paratype X 359. 

2c. Lateral view of paratype X 359. 3a. Oral view of paratype X 551. 3b. Aboral view of 
paratype X 551. 3c. Lateral view of paratype X 551. 

Figs. 4-6. Polygnathus inornatus inornatus Branson & Mehl 

4a. Aboral view of specimen X 353. 4b. Oral view of specimen X 353. 4c. Lateral view of 
specimen X 353. 5a. Aboral view of specimen X 355. 5b. Oral view of specimen X 355. 
5c. Lateral view of specimen X 355. 6a. Oral view of specimen X 354. 6b. Aboral view of 
specimen X 354. 6c. Lateral view of specimen X 354. 

Figs. 7-9. Polygnathus inornatus rostratus subsp. nov. 

7a. Aboral view of holotype X 530. 7b. Oral view of holotype X 530. 7c. Lateral view of 

holotype X 530. 8a. Aboral view of paratype X 357. 8b. Oral view of paratype X 357. 

9a. Aboral view of paratype X 356. 9b. Oral view of paratype X 356. 9c. Lateral view of 
paratype X 356. 



Bull. By. Mus. nat. Hist. (Geol. Suppl.) 5 



PLATE 10 




PLATE ii 
All specimens coated and magnified x 31.5 

Figs. 1-4. Polygnathus lacinatus asymtnetricus subsp. nov. 

ia. Aboral view of paratype X 360. ib. Oral view of paratype X 360. ic. Lateral view of 
paratype X 360. 2a. Aboral view of paratype X 363. 2b. Oral view of paratype X 363. 
2C. Lateral view of paratype X 363. 3a. Aboral view of holotype X 361. 3b. Oral view of 
holotype X 361. 3c Lateral view of holotype X 361. 4a. Aboral view of paratype X 362. 
4b. Oral view of paratype X 362. 4c. Lateral view of paratype X 362. 

Figs. 5-7, 11. Polygnathus lacinatus prelobatus subsp. nov. 

5a. Oral view of paratype X 372. 5b. Aboral view of paratype X 372. 6a. Oral view of 
paratype X 374. 6b. Aboral view of paratype X 374. 7a. Oral view of paratype X 373. 
7b. Lateral view of paratype X 373. 11a. Oral view of holotype X 371. nb. Aboral view 
of holotype X 371. 11c. Lateral view of holotype X 371. 

Figs. 8-10. Polygnathus lacinatus lacinatus Huddle 

8a. Oral view of specimen X 370. 8b. Lateral view of specimen X 370. 9a. Oral view of 
specimen X 369. 9b. Aboral view of specimen X 369. 9c. Lateral view of specimen X 369. 
10a. Aboral view of specimen X 368. 10b. Oral view of specimen X 368. 10c. Lateral view 
of specimen X 368 . 

Figs. 12-15. Polygnathus lacinatus circaperipherus subsp. nov. 

12a. Aboral view of paratype X 367. 12b. Oral view of paratype X 367. 12c. Lateral view 
of paratype X 367. 13a. Aboral view of paratype X 365. 13b. Oral view of paratype X 365. 
13c. Lateral view of paratype X 365. 14a. Aboral view of holotype X 364. 14b. Oral view of 
holotype X 364. 14c. Lateral view of holotype X 364. 15a. Oral view of paratype X 366. 
15b. Aboral view of paratype X 366. 15c. Lateral view of paratype X 366. 



Bull. Br. Mus. nat. Hist. (Geol. Suppl.) 5 



PLATE 11 




PLATE 12 
All specimens coated and magnified x 31.5 

Fig. 1. Polygnathus cf. communis Branson & Mehl 

a. Aboral view of specimen X 516. b. Oral view of specimen X 516. c. Lateral view of 
specimen X 516. 

Figs. 2-5. Polygnathus communis communis Branson & Mehl 

2a. Oral view of specimen X 348. 2b. Aboral view of specimen X 348. 2c. Lateral view of 
specimen X 348. 3a. Oral view of specimen X 347. 3b. Aboral view of specimen X 347. 
3c. Lateral view of specimen X 347. 4a. Aboral view of specimen X 430. 4b. Oral view of 
specimen X 430. 4c. Lateral view of specimen X 430. 5a. Oral view of specimen X 346. 
5b. Aboral view of specimen X 346. 5c. Lateral view of specimen X 346. 

Figs. 6-8, 10. Pseudopolygnathus nodomarginatus (E. R. Branson) 

6a. Oral view of specimen X 495. 6b. Aboral view of specimen X 495. 6c. Lateral view of 
specimen X 495. 7a. Aboral view of specimen X 493. 7b. Oral view of specimen X 493. 
7c. Lateral view of specimen X 493. 8a. Oral view of specimen X 494 showing rounding of 
posterior termination. 8b. Aboral view of specimen X 494 showing rounding of posterior 
termination. 8c. Lateral view of specimen X 494. 10a. Aboral view of specimen X 492. 
10b. Oral view of specimen X 492. 10c. Lateral view of specimen X 492. 

Figs. 9, 11. Siphonodella isosticha (Cooper) 

9a. Oral view of specimen X 534. 9b. Aboral view of specimen X 534. 11a. Oral view of 
specimen X 535. lib. Aboral view of specimen X 535. 

Fig. 12. Siphonodella sp. A 
a. Aboral view of specimen X 537. b. Oral view of specimen X 537. 

Fig. 13. Siphonodella obsoleta Hass 

a. Aboral view of specimen X 536. b. Oral view of specimen X 536. c. Lateral view of 
specimen X 536. 



Bull. Br. Mus. nat. Hist. (Geol. Suppl.) 5. 



PLATE 12 




PLATE 13 
All specimens coated and magnified x 31.5 

Figs. 1-3. Taphrognathus - Cavusgnathus transitions 

1. Oral view of specimen X 558. 2. Oral view of specimen X 559. 3a. Oral view of specimen 
X 560. 3b. Aboral view of specimen X 560. 3c. Outer lateral view of specimen X 560. 

Figs. 4, 5. Taphrognathus varians Branson & Mehl 

4a. Oral view of specimen X 407. 4b. Aboral view of specimen X 407. 4c. Outer lateral 
view of specimen X 407. 4d. Inner lateral view of specimen X 407. 5a. Oral view of specimen 
X 408. 5b. Aboral view of specimen X 408. 5c. Outer lateral view of specimen X 408. 
5d. Inner lateral view of specimen X 408. 

Figs. 6, 7, 13. Cavusgnathus charactus Rexroad 

6a. Oral view of specimen X 59. 6b. Aboral view of specimen X 59. 6c. Outer lateral view 
of specimen X 59. 6d. Inner lateral view of specimen X 59. 7a. Oral view of specimen X 61. 
7b. Aboral view of specimen X 61. 7c. Outer lateral view of specimen X 61 . 7d. Inner lateral 
view of specimen X 61. 13a. Oral view of specimen X 62. 13b. Aboral view of specimen 
X 62. 13c. Inner lateral view of specimen X 62. 

Figs. 8-1 i. Polygnathus bischoffi sp. nov. 

8a. Oral view of hypotype X 352. 8b. Aboral view of hypotype X 352. 8c. Lateral view of 
hypotype X 352. 9a. Oral view of paratype X 351. 9b. Aboral view of paratype X 351. 
9c. Lateral view of paratype X 351. 10a. Oral view of paratype X 350. 10b. Aboral view 
of paratype X 350. 10c. Lateral view of paratype X 350. 11a. Oral view of holotype X 349. 
11b. Aboral view of holotype X 349. 11c. Lateral view of holotype X 349. 

Fig. 12. Cavusgnathus naviculus (Hinde) 

a. Oral view of specimen X 65. b. Outer lateral view of specimen X 65. c. Aboral view of 
specimen X 65. d. Inner lateral view of specimen X 65. 



Bull. Br. Mus. nat. Hist. (Geol. Suppl.) 5 



PLATE 13 




PLATE 14 
All specimens coated and magnified x 31.5 

Figs, i, 4-6. Cavusgnathus naviculus (Hinde) 

ia. Oral view of specimen X 66. ib. Aboral view of specimen X 66. ic. Inner lateral view 
of specimen X 66. id. Outer lateral view of specimen X 66. 4a. Oral view of specimen 
X 69. 4b. Aboral view of specimen X 69. 4c. Inner lateral view of specimen X 69. 4d. 
Outer lateral view of specimen X 69. 5a. Oral view of specimen X 68. 5b. Aboral view of 
specimen X 68. 5c. Inner lateral view of specimen X 68. 5d. Outer lateral view of specimen 
X 68. 6a. Oral view of specimen X 67. 6b. Aboral view of specimen X 67. 6c. Inner lateral 
view of specimen X 67. 6d. Outer lateral view of specimen X 67. 

Fig. 2. Cavusgnathus convexus Rexroad 

a. Oral view of specimen X 63. b. Aboral view of specimen X 63. c. Inner lateral view of 
specimen X 63. d. Outer lateral views of specimen X 63. 

Fig. 3. Cavusgnathus cristatus Branson and Mehl 

a. Oral view of specimen X 64. b. Aboral view of specimen X 64. c. Inner lateral view of 
specimen X 64. d. Outer lateral view of specimen X 64. 



Bull. Br. Mus. nat. Hist. (Geol. Suppl.) 5 



PLATE 14 




PLATE 15 
All specimens coated and magnified x 31.5 

Figs. 1-3, 8. Mestognathus bipluti Higgins 

ia. Outer aboral lateral view of specimen X 246. ib. Outer lateral oral view of specimen 
X 246. ic. Inner lateral oral view of specimen X 246. 2a. Aboral view of specimen X 248. 
2b. Outer lateral view of specimen X 248. 2c. Inner lateral view of specimen X 248. 3a. 
Outer aboral lateral view of specimen X 247. 3b. Outer lateral oral view of specimen X 247. 
3c. Inner lateral oral view of specimen X 247. 8a. Aboral view of specimen X 249. 8b. Inner 
oral view of specimen X 249. 

Figs. 4-6. Mestognathus neddensis sp. nov. 

4a. Aboral view of paratype X 251. 4b. Inner lateral oral view of paratype X 251. 4c. Outer 
lateral view of paratype X 251. 5a. Outer aboral lateral view of paratype X 252. 5b. Inner 
lateral oral view of paratype X 252. 5c. Outer lateral oral view of paratype X 252. 6a. Aboral 
view of holotype X 250. 6b. Inner lateral oral view of holotype X 250. 6c. Outer lateral 
view of holotype X 250. 

Fig. 7. Mestognathus beckmanni Bischoff 

a. Aboral view of specimen X 245. b. Oral view of specimen X 245. c. Outer lateral view 
of specimen X 245. d. Inner lateral view of specimen X 245. 

Fig. 9. Polygnathus sp. 

a. Oral view of specimen X 531. b. Inner lateral view of specimen X 531. c. Aboral view 
of specimen X 531. 



Bull. Br. Mus. nat. Hist. (Geol. Suppl.) 5 



PLATE 15 




PLATE 16 
All specimens coated and magnified x 31.5 

Figs. 1-4. Gnathodus girtyi simplex Dunn 



ia. Aboral view of specimen X 108. ib. Oral view of specimen X 108. ic. Outer lateral 
view of specimen X 108. id. Inner lateral view of specimen X 108. 2a. Oral view of specimen 
X 107. 2b. Aboral view of specimen X 107. 2c. Inner lateral view of specimen X 107. 
2d. Outer lateral view of specimen X 107. 3a. Oral view of specimen X no. 3b. Aboral 
view of specimen X no. 3c. Inner lateral view of specimen X no. 3d. Outer lateral view 
of specimen X no. 4a. Oral view of specimen X in. 4b. Aboral view of specimen X in. 
4c. Inner lateral view of specimen X in. 4d. Outer lateral view of specimen X in. 

Figs. 5-8. Gnathodus girtyi collinsoni subsp. nov. 

5a. Oral view of paratype X 102. 5b. Aboral view of paratype X 102. 5c. Inner lateral 
view of paratype X 102. 5d. Outer lateral view of paratype X 102. 6a. Aboral view of 
holotype X 99. 6b. Oral view to holotype X 99. 6c. Outer lateral view of holotype X 99. 
6d. Inner lateral view of holotype X 99. 7a. Aboral view of paratype X 101. 7b. Oral view 
of paratype X 101. 7c. Outer lateral view of paratype X 101. 7d. Inner lateral view of 
paratype X 101. 8a. Aboral view of paratype X 100. 8b. Oral view of paratype X 100. 
8c. Outer lateral view of paratype X 100. 8d. Inner lateral view of paratype X 100. 



Bull. Br. Mus. nat. Hist. (Geol. Suppl.) 5 



PLATE 16 



2c 3 C 

ggm^^ ^gH^ ^^|||tttt[ :^mmk 



mum mmm mm* 



»1,l*lfj'; 



/jK^jjjttf| i^^^^k tiMSE^ 



PLATE 17 
All specimens coated and magnified x 31.5 

Figs. 1-3. Gnathodus girtyi subsp. nov. A 

1 a. Aboral view of specimen X 118. ib. Oral view of specimen X 118. ic. Inner lateral 
view of specimen X 118. 2a. Aboral view of specimen X 119. 2b. Oral view of specimen 
X 119. 2C. Outer lateral view of specimen X 119. 2d. Inner lateral view of specimen X 119. 
3a. Aboral view of specimen X 117. 3b. Oral view of specimen X 117. 3c. Outer lateral 
view of specimen X 117. 3d. Inner lateral view of specimen X 117. 

Fig. 4. Gnathodus sp. 

a. Aboral view of specimen X 138. b. Oral view of specimen X 138. c. Inner lateral view of 
specimen X 138. d. Outer lateral view of specimen X 138. 

Figs. 5-8. Gnathodus girtyi soniae subsp. nov. 

5a. Aboral view of paratype X 115. 5b. Oral view of paratype X 115. 5c. Outer lateral 
view of paratype X 115. 5d. Inner lateral view of paratype X 115. 6a. Aboral view of 
holotype X 113. 6b. Oral view of holotype X 113. 6c. Outer lateral view of holotype X 113. 
7a. Aboral view of paratype X 112. 7b. Oral view of paratype X 112. 7c. Outer lateral 
view of paratype X 112. 7d. Inner lateral view of paratype X 112. 8a. Oral view of paratype 
X 114. 8b. Aboral view of paratype X 114. 8c. Inner lateral view of paratype X 114. 
8d. Outer lateral view of paratype X 114. 

Figs. 9-12. Gnathodus girtyi girtyi Hass 

9a. Aboral view of specimen X 106. 9b. Oral view of specimen X 106. 9c. Outer lateral 
view of specimen X 106. gd. Inner lateral views of specimen X 106. 10a. Aboral view of 
specimen X 105. 10b. Oral view of specimen X 105. 10c. Outer lateral view of specimen 
X 105. iod. Inner lateral view of specimen X 105. na. Aboral view of specimen X 104. 
11b. Oral view of specimen X 104. 11c. Outer lateral view of specimen X 104. nd. Inner 
lateral view of specimen X 104. 12a. Aboral view of specimen X 103. 12b. Oral view of 
specimen X 103. 12c. Outer lateral view of specimen X 103. i2d. Inner lateral view of 
specimen X 103. 



Bull. Dr. Mus. nat. Hist. (Geol. Suppl.) 5 



PLATE 




PLATE 1 8 
All specimens coated and magnified x 31.5 

Figs, i, 10, n. Gnathodus punctatus (Cooper) 

ia. Aboral view of specimen X 132. ib. Oral view of specimen X 132. ic. Outer lateral 
view of specimen X 132. 10a. Aboral view of specimen X 131. 10b. Oral view of specimen 
X 131. ioc. Inner lateral view of specimen X 131. iod. Outer lateral view of specimen 
X 131. 11a. Aboral view of specimen X 133. lib. Oral view of specimen X 133. 11c. Inner 
lateral view of specimen X 133. nd. Outer lateral view of specimen X 133. 

Figs. 2-5. Gnathodus simplicatus sp. now 

2a. Aboral view of holotype X 89. 2b. Oral view of holotype X 89. 2c. Lateral view of 
holotype X 89. 3a. Lateral view of paratype X 91. 3b. Oral view of paratype X 91. 4a 
Lateral view of paratype X 90. 4b. Oral view of paratype X 90. 5a. Lateral view of 
paratype X 415. 5b. Oral view of paratype X 415. 

Figs. 6, 8, 13. Gnathodus antetexanus Rexroad & Scott 

6a. Aboral view of specimen X 412. 6b. Oral view of specimen X 412. 6c. Outer lateral 
view of specimen X 412. 8a. Outer lateral view of specimen X 413. 8b. Oral view of specimen 
X 413. 13a. Aboral view of specimen X 414. 13b. Oral view of specimen X 414. 13c. Outer 
lateral view of specimen X 414. 13d. Inner lateral view of specimen X 414. 

Fig. 7. Gnathodus ? sp. nov. 

a. Aboral view of specimen X 92. b. Oral view of specimen X 92. c. Outer lateral view of 
specimen X 92. 

Fig. 9. Gnathodus avonensis sp. nov. 

a. Aboral view of holotype X 411. b. Oral view of holotype X 411. c. Lateral view of 
holotype X 411. d. Lateral view of holotype X 411. 

Fig. 12. Gnathodus delicatus Branson & Mehl 

a. Aboral view of specimen X 87. b. Oral view of specimen X 87. c. Inner lateral view of 
specimen X 87. d. Outer lateral view of specimen X 87. 

Figs. 14-17. Gnathodus bilineatus (Roundy) 

14a. Aboral view of specimen X 94. 14b. Oral view of specimen X 94. 14c. Outer lateral 
view of specimen X 94. i4d. Inner lateral view of specimen X 94. 15a. Aboral view of 
specimen X 93. 15b. Oral view of specimen X 93. 15c. Inner lateral view of specimen X 93. 
I5d. Outer lateral view of specimen X 93. 16a. Aboral view of specimen X 417. 16b. Oral 
view of specimen X 417. 16c. Inner lateral view of specimen X 417. i6d. Outer lateral view 
of specimen X 417. 17a. Aboral view of specimen X 416. 17b. Oral view of specimen 
X 416. 17c. Inner lateral view of specimen X 416. i7d. Outer lateral view of specimen 
X 416. 



Bull. By. Mus. nat. Hist. (Geol. Suppl.) 5 



PLATE ]8 




PLATE 19 
All specimens coated and magnified x 31.5 

Figs. 1-4. Gnathodus symmutatus sp. nov. 

ia. Lateral view of paratype X 135. ib. Aboral view of paratype X 135. 2a. Oral view of 
para type X 136. 2b. Lateral view of paratype X 136. 2c. Aboral view of paratype X 136. 
3a. Lateral view of paratype X 137. 3b. Aboral view of paratype X 137. 4a. Lateral view 
of holotype X 134. 4b. Aboral view of holotype X 134. 4c. Oral view of holotype X 134. 

Figs. 5-8. Gnathodus homopunctatus Ziegler 

5a. Lateral view of specimen X 121. 5b. Lateral view of specimen X 121. 5c. Oral view of 
specimen X 121. d. Aboral view of specimen X 121. 6a. Lateral view of specimen X 122. 
6b. Lateral view of specimen X 122. 6c. Oral view of specimen X 122. 6d. Aboral view of 
specimen X 122. 7a. Lateral view of specimen X 123. 7b. Lateral view of specimen X 123. 
7c. Aboral view of specimen X 123. 7d. Oral view of specimen X 123. 8a. Lateral view of 
specimen X 120. 8b. Lateral view of specimen X 120. 8c. Aboral view of specimen X 120. 
8d. Oral view of specimen X 120. 

Figs. 9-12. Gnathodus commutatus (Branson & Mehl) 

9a. Lateral view of specimen X 96. 9b. Lateral view of specimen X 96. gc. Aboral view of 
specimen X 96. gd. Oral view of specimen X 96. 10a. Lateral view of specimen X 418. 
10b. Lateral view of specimen X 418. 10c. Aboral view of specimen X 418. iod. Oral view 
of specimen X 418. na. Lateral view of specimen X 95. 11b. Lateral view of specimen 
X 95. lie. Aboral view of specimen X 95. nd. Oral view of specimen X 95. 12a. Lateral 
view of specimen X 97. 12b. Lateral view of specimen X 97. 12c. Oral view of specimen 
X 97. i2d. Aboral view of specimen X 97. 



Figs. 13-15. Gnathodus tnononodosus sp. nov. 

13a. Lateral view of paratype X 126. 13b. Lateral view of paratype X 126. 13c. Oral view 
of paratype X 126. 13d. Aboral view of paratype X 126. 14a. Lateral view of holotype 
X 124. 14b. Lateral view of holotype X 124. 14c. Aboral view of holotype X 124. I4d. 
Oral view of holotype X 124. 15a. Lateral view of paratype X 125. 15b. Lateral view of 
paratype X 125. 15c. Aboral view of paratype X 125. 13d. Oral view of paratype X 125. 



Figs. 16-20. Gnathodus nodosus Bischoff 

16a. Lateral view of specimen X 128. 16b. Lateral view of specimen X 128. 16c. Aboral 
view of specimen X 128. i6d. Oral view of specimen X 128. 17a. Lateral view of specimen 
X 509. 17b. Lateral view of specimen X 509. 17c. Aboral view of specimen X 509. I7d. 
Oral view of specimen X 509. 18a. Lateral view of specimen X 510. 18b. Lateral view of 
specimen X 510. 18c. Aboral view of specimen X 510. i8d. Oral view of specimen X 510. 
19a. Lateral view of specimen X 129. 19b. Lateral view of specimen X 129. 19c. Aboral 
view of specimen X 129. I9d. Oral view of specimen X 129. 20a. Lateral view of specimen 
X 127. 20b. Aboral view of specimen X 127. 20c. Oral view of specimen X 127. 



Bull. Br. Mus. nat. Hist. (Geol. Suppl.) 5 



PLATE 19 



PLATE 20 
All specimens coated and magnified x 31.5 

Figs. 1-2. Apatognathus chauliodus Varker 

ia. Inner lateral view of specimen X 44. ib. Outer lateral view of specimen X 44. 2a. Inner 
lateral view of specimen X 550. 2b. Outer lateral view of specimen X 550. 

Figs. 3, 4, 6, 7. Apatognathus geminus (Hinde) 

3a. Inner lateral view of specimen X 55. 3b. Outer lateral view of specimen X 55. 4a. Inner 
lateral view of specimen X 54. 4b. Outer lateral view of specimen X 54. 6a. Outer lateral 
view of specimen X 56. 6b. Inner lateral view of specimen X 56. 7a. Inner lateral view of 
specimen X 57. 7b. Outer lateral view of specimen X 57. 

Fig. 5. Apatognathus various Branson & Mehl 
a. Inner lateral view of specimen X 42. b. Outer lateral view of specimen X 42. 

Fig. 8. Apatognathus cf. libratus Varker 
a. Inner lateral view of specimen X 58. b. Outer lateral view of specimen X 58. 

Figs. 9-1 1. Apatognathus scalenus Varker 

9a. Inner lateral view of specimen X 48. 9b. Outer lateral view of specimen X 48. 10a. Inner 
lateral view of specimen X 49. 10b. Outer lateral view of specimen X 49. 11a. Inner lateral 
view of specimen X 47. 11b. Outer lateral view of specimen X 47. 

Figs. 12-14, x 7- Apatognathus petilus Varker 

12a. Outer lateral view of specimen X 51. 12b. Inner lateral view of specimen X 51. 13a. 
Inner lateral view of specimen X 52. 13b. Outer lateral view of specimen X 52. 14a. Inner 
lateral view of specimen X 50. 14b. Outer lateral view of specimen X 50. 17a. Inner lateral 
view of specimen X 53. 17b. Outer lateral view of specimen X 53. 

Figs. 15-16. Apatognathus bladus sp. nov. 

15a. Inner lateral view of paratype X 46. 15b. Outer lateral view of paratype X 46. 16a. 
Inner lateral view of holotype X 45. 16b. Outer lateral view of holotype X 45. 



Bull. Br. Mus. nat. Hist. (Geol. Suppl.) 5 



PLATE 20 




PLATE 21 
All specimens coated and magnified x 31.5 

Fig. 1. Neoprioniodus cf. confluens (Branson & Mehl) 

a. Lateral view of specimen X 520. b. Aboral view of specimen X 520. c. Oral view of 
specimen X 520. 

Figs. 2, 8. Neoprioniodus confluens (Branson & Mehl) 

2a. Outer lateral view of specimen X 264. 2b. Inner lateral view of specimen X 264. 8a. 
Inner lateral view of specimen X 263. 8b. Outer lateral view of specimen X 263. 

Fig. 3. Neoprioniodus cf. armatus (Hinde) 

a. Inner lateral view of specimen X 283. b. Aboral view of specimen X 283. c. Oral view of 
specimen X 283. 

Figs. 4-7. Neoprioniodus barbatus (Branson & Mehl) 

4. Lateral view of specimen X 259. 5a. Lateral view of specimen X 260. 5b. Aboral view 
of specimen X 260. 6. Lateral view of specimen X 262. 7. Lateral view of specimen X 261. 

Fig. 9. Neoprioniodus spathatus Higgins 
a. Outer lateral view of specimen X 279. b. Inner lateral view of specimen X 279. 

Figs, io-ii. Neoprioniodus antespathatus Collinson and Druce 

10a. Outer lateral view of specimen X 258. 10b. Inner lateral view of specimen X 258. 
11a. Inner lateral view of specimen X 257. lib. Outer lateral view of specimen X 257. 

Figs. 12-15. Neoprioniodus peracutus (Hinde) 

12a. Inner lateral view of specimen X 273. 12b. Outer lateral view of specimen X 273. 

13a. Outer lateral view of specimen X 275. 13b. Inner lateral view of specimen X 275. 

14a. Inner lateral view of specimen X 274. 14b. Outer lateral view of specimen X 274. 

15a. Outer lateral view of specimen X 272. 15b. Inner lateral view of specimen X 272. 

Figs. 16, 17, 20. Neoprioniodus conjunctus (Gunnell) 

16a. Inner lateral view of specimen X 265. 16b. Outer lateral view of specimen X 265. 
17a. Outer lateral view of specimen X 266. 17b. Inner lateral view of specimen X 266. 
20a. Inner lateral view of specimen X 267. 20b. Outer lateral view of specimen X 267. 

Fig. 18. Neoprioniodus varians (Branson & Mehl) 
a. Outer lateral view of specimen X 281. b. Inner lateral view of specimen X 281. 

Fig. 19. Neoprioniodus tulensis (Pander) 
a. Outer lateral view of specimen X 280. b. Inner lateral view of specimen X 280. 



Bull. Br. Mus. nat. Hist. (Geol. Suppl.) 5 



PLATE 21 




PLATE 22 

All specimens coated and magnified x 31.5 

Figs. 1-4. Neoprioniodus cf. camurus Rexroad 

ia. Inner lateral view of specimen X 285. ib. Outer lateral view of specimen X 285. 2a. 
Inner lateral view of specimen X 287. 2b. Outer lateral view of specimen X 287. 3a. Inner 
lateral view of specimen X 284. 3b. Outer lateral view of specimen X 284. 4a. Inner lateral 
view of specimen X 286. 4b. Outer lateral view of specimen X 286. 

Figs. 5-8. Neoprioniodus montanaensis (Scott) 

5a. Outer lateral view of specimen X 271. 5b. Inner lateral view of specimen X 271. 6a. 
Inner lateral view of specimen X 269. 6b. Outer lateral view of specimen X 269. 7a. Outer 
lateral view of specimen X 268. 7b. Inner lateral view of specimen X 268. 8a. Outer lateral 
view of specimen X 270. 8b. Inner lateral view of specimen X 270. 

Figs, g, 10, 12. Neoprioniodus scitulus (Branson & Mehl) 

9a. Lateral view of specimen X 277. 9b. Lateral view of specimen X 277. 10a. Lateral view 
of specimen X 276. 10b. Lateral view of specimen X 276. 12a. Lateral view of specimen 
X 278. 12b. Lateral view of specimen X 278. 

Fig. 11. Euprioniodina caverna (Collinson & Druce) 
a. Outer lateral view of specimen X 83. b. Inner lateral view of specimen X 83. 

Fig. 13. Euprioniodina sp. nov. A 
a. Inner lateral view of specimen X 86. b. Outer lateral view of specimen X 86. 

Fig. 14. Neoprioniodus sp. nov. A 
Inner lateral view of specimen X 282. 

Fig. 15. Euprioniodina sp. 
a. Inner lateral view of specimen X 85. b. Outer lateral view of specimen X 85. 

Fig. 16. Euprioniodina microdentata (Ellison) 
a. Inner lateral view of specimen X 84. b. Outer lateral view of specimen X 84. 

Fig. 17-20. Hindeodus sp. 

17a. Outer lateral view of specimen X 191. 17b. Inner lateral view of specimen X 191. 18a. 
Outer lateral view of specimen X 189. 18b. Inner lateral view of specimen X 189. 19a. Outer 
lateral view of specimen X 188. 19b. Inner lateral view of specimen X 188. 20a. Inner 
Literal view of specimen X 190. 20b. Outer lateral view of specimen X 190. 



Bull. Br. Mus. nat. Hist. (Geol. Suppl.) 5 



PLATE 22 



- la 1b^ 2o 2 b 3a . 3b f. ol 4b 



12a 12b 



13a 13b 



] 6a i 6 b 



PLATE 23 
All specimens coated and magnified x 31.5 

Figs. 1-2. Kladognathus clarensis Collinson and Druce 

ia. Outer lateral view of specimen X 196. ib. Inner lateral view of specimen X 196. 2a. 
Inner lateral view of specimen X 195. 2b. Outer lateral view of specimen X 195. 

Figs. 3-6. Kladognathus tnacrodentatus (Higgins) 

3a. Inner lateral view of specimen X 197. 3b. Outer lateral view of specimen X 197. 3c. 
Oral view of specimen X 197. 4a. Inner lateral view of specimen X 198. 4b. Outer lateral 
view of specimen X 198. 4c. Oral view of specimen X 198. 5a. Outer lateral view of specimen 
X 199. 5b. Inner lateral view of specimen X 199. 5c. Oral view of specimen X 199. 6a. 
Inner lateral view of specimen X 200. 6b. Outer lateral view of specimen X 200. 6c. Oral 
view of specimen X 200. 

Fig. 7. Magnilaterella ? sp. 
a. Inner lateral view of specimen X 447. b. Outer lateral view of specimen X 447. 

Figs. 8, 18. Magnilaterella contraria sp. nov. 

8a. Inner lateral view of holotype X 553. 8b. Aboral view of holotype X 553. 8c. Outer 
lateral view of holotype X 553. 18a. Outer lateral view of paratype X 517. 18b. Inner 
lateral view of paratype X 517. 18c. Aboral view of paratype X 517. 

Fig. 9, 10. Magnilaterella spp. 
9. Inner lateral view of specimen X 244. 10. Inner lateral view of specimen X 242. 

Figs. 11-13. Magnilaterella clarkei sp. nov 

11. Inner lateral view of paratype X 241. 12. Inner lateral view of holotype X 431. 13a. 
Outer lateral view of paratype X 432. 13b. Inner lateral view of paratype X 432. 

Figs. 14-17. Magnilaterella complectens (Clarke) 

14a. Outer lateral view of specimen X 238. 14b. Aboral view of specimen X 238. 14c. Inner 
lateral view of specimen X 238. 15a. Inner lateral view of specimen X 239. 15b. Aboral view 
of specimen X 239. 15c. Outer lateral view of specimen X 239. 16a. Outer lateral view of 
specimen X 240. 16b. Aboral view of specimen X 240. 16c. Inner lateral view of specimen 
X 240. 17a. Outer lateral view of specimen X 237. 17b. Inner lateral view of specimen 
X 237. 17c. Aboral view of specimen X 237. 



Bull. Br. Mus. nat. Hist. (Geol. Suppl.) 5 



PLATE 23 




PLATE 24 
All specimens coated and magnified x 31.5 

Figs. 1-6. Prioniodina prelaevipostica sp. nov. 

1. Inner lateral view oi paratype X 333. 2. Inner lateral view of paratype X 332. 3a. Inner 
lateral view of paratype X 331. 3b. Oral view of paratype X 331. 3c. Aboral view of 
paratype X 331. 4a. Inner lateral view of holotype X 334. 4b. Oral view of holotype X 334. 
4c. Aboral view of holotype X 334. 5. Inner lateral view of paratype X 335. 6. Inner 
lateral view of paratype X 336. 

Fig. 7. Lonchodina obtunda Collinson & Druce 

a. Inner lateral view of specimen X 229. b. Oral view of specimen X 229. c. Aboral view of 
specimen X 229. 

Figs. 8-1 1. Metalonchodina bidentata (Gunnell) 

8a. Outer lateral view of specimen X 256. 8b. Inner lateral view of specimen X 256. 9a. 
Inner lateral view of specimen X 253. 9b. Outer lateral view of specimen X 253. 9c. Aboral 
view of specimen X 253. 10a. Inner lateral view of specimen X 254. 10b. Outer lateral 
view of specimen X 254. ua. Outer lateral view of specimen X 255. lib. Inner lateral 
view of specimen X 255. 

Figs. 12-14. Lonchodina bolbosa Collinson & Druce 

12a. Oral view of specimen X 223. 12b. Aboral view of specimen X 223. 13a. Oral view of 
specimen X 222. 13b. Aboral view of specimen X 222. 13c. Lateral view of specimen X 222. 
14a. Oral view of specimen X 224. 14b. Aboral view of specimen X 224. 

Figs. 15, 18. Lonchodina paraclaviger Rexroad 

15a. Aboral view of specimen X 233. 15b. Oral view of specimen X 233. 18a. Oral view of 
specimen X 232. 18b. Aboral view of specimen X 232. 

Fig. 16. Lonchodina paraclarki Hass 
a. Aboro-lateral view of specimen X 231. b. Inner lateral view of specimen X 231. 

Fig. 17. Lonchodina sp. A 

a. Aboro-lateral view of specimen X 424. b. Oral view of specimen X 424. 

Fig. 19. Prioniodina latericrescens (Branson & Mehl) 
Inner lateral view of specimen X 429. 

Figs. 20-23. Lonchodina fur nis hi Rexroad 

20a. Inner lateral view of specimen X 227. 20b. Aboral view of specimen X 227. 20c. Oral 
view of specimen X 227. 21a. Lateral view of specimen X 226. 21b. Aboral view of specimen 
X 226. 21c. Oral view of specimen X 226. 22a. Lateral view of specimen X 225. 22b. Oral 
view of specimen X 225. 22c. Aboral view of specimen X 225. 23a. Lateral view of specimen 
X 228. 23b. Aboro-lateral view of specimen X 228. 23c. Oral view of specimen X 228. 



Bull. By. Mus. nat. Hist. (Geo!. Suppl.) 5 



PLATE 24 




I'LATE 25 
All specimens coated and magnified x 31.5 

Fig. 1. Hibbardella (Roundya) sp. 
Lateral view of specimen X 423. 

Figs. 2-5. Hibbardella (Roundya) barnettana Hass 

2a. Aboro-lateral view of specimen X 154. 2b. Lateral view of specimen X 154. 3a. Anterior 
view of specimen X 152. 3b. Posterior view of specimen X 152. 4a. Postero-lateral view of 
specimen X 151. 4b. Lateral view of specimen X 151. 5a. Lateral view of specimen X 153. 
5b. Aboral view of specimen X 153. 

Fig. 6. Gen. nov. A sp. 
a. Lateral view of specrmen X 409. b. Oral view of specimen X 409. 

Fig. 7. Gen. nov. B sp. 
a. Lateral view of specimen X 410. b. Aboral view of specimen X 410. 

Figs. 8, 9. Plectospat nodus ? sp. nov. A 

8a. Inner lateral view of specimen X 313. 8b. Oral view of specimen X 313. 9. Inner lateral 
view of specimen X 312. 

Figs. 10-12. Plectospathodus ? sp. nov. B 

10. Inner lateral view of specimen X 427. n. Inner lateral view of specimen X 428. 12. 
Inner lateral view of specimen X 314. 

Figs. 13-14. Hibbardella (Hassognathus) separata (Branson & Mehl) 

13a. Lateral view of specimen X 150. 13b. Aboral view of specimen X 150. 13c. Posterior 
view of specimen X 150. 14. Lateral view of specimen X 149. 

Fig. 15. Hibbardella (Hibbardella) sp. 

a. Posterior view of specimen X 441. b. Anterior view of specimen X 441. 

Figs. 16-18. Hibbardella (Hibbardella) cf. macrodentata Thomas 

16a. Posterior view of specimen X 147. 16b. Oral view of specimen X 147. 17a. Lateral view 
of specimen X 146. 17b. Posterior view of specimen X 146. 18a. Lateral view of specimen 
X 148. 18b. Oral view of specimen X 148. 18c. Posterior view of specimen X 148. 

Figs. 19-20. Hibbardella (Hibbardella) acuta Murray & Chronic 

19a. Posterior view of specimen X 139. 19b. Anterior view of specimen X 139. 20. Lateral 
view of specimen X 422. 

Fig. 21. Hibbaradella (Hibbardella) parva sp. nov. 
a. Anterior view of holotype X 144. b. Posterior view of holotype X 144. 

Fig. 22. Hibbardella (Hibbardella) ortha Rexroad 
a. Posterior view of specimen X 143. b. Anterior view of specimen X 143. 

Figs. 23-25. Hibbardella (Hibbardella) milleri Rexroad 

23a. Anterior view of specimen X 140. 23b. Posterior view of specimen X 140. 24a. Anterior 
view of specimen X 141. 24b. Aboral view of specimen X 141. 24c. Posterior view of 
specimen X 141. 25a. Anterior view of specimen X 142. 25b. Posterior view of specimen 
X 142. 



Bull. Br. Mus. nat. Hist. (Geol. Suppl.) 5 



PLATE 25 




PLATE 26 
All specimens coated and magnified x 31.5 

Figs. 1-2. Ligonodina osborni sp. nov. 

ia. Outer lateral view of holotype X 212. ib. Posterior view of holotype X 212. ic. Inner 
lateral view of holotype X 212. 2a. Outer lateral view of paratype X 213. 2b. Posterior 
view of paratype X 213. 2c. Inner lateral view of paratype X 213. 

Fig. 3. Ligonodina sp. A 

3a. Inner lateral view of specimen X 217. 3b. Oral view of specimen X 217. 3c. Aboral view 
of specimen X 217. 

Figs. 4-6. Ligonodina beata nom. nov. 

4. Inner lateral view of specimen X 203. 5a. Inner lateral view of specimen X 201. 5b. Oral 
view of specimen X 201. 5c. Aboral view of specimen X 201. 6a. Inner lateral view of 
specimen X 202. 6b. Aboral view of specimen X 202. 

Fig. 7. Ligonodina ? sp. 
Inner lateral view of specimen X 218. 

Figs. 8-1 i. Ligonodina magnilaterina sp. nov. 

8a. Inner lateral view of paratype X 210. 8b. Outer lateral view of paratype X 210. 9a. 
Outer lateral view of paratype X 208. gb. Inner lateral view of paratype X 208. 10a. Inner 
lateral view of paratype X 209. 10b. Outer lateral view of paratype X 209. 11a. Outer 
lateral view of holotype X 211. lib. Inner lateral view of holotype X 211. 

Fig. 12. Ligonodina ? sp. 
a. Aboral view of specimen X 219. b. Inner lateral view of specimen X 219. 

Figs. 13, 14, 16. Ligonodina roundyi Hass 

13a. Inner lateral view of specimen X 216. 13b. Posterior view of specimen X 216. 13c. 
Aboral view of specimen X 216. 14a. Postero-lateral view of specimen X 214. 14b. Posterior 
view of specimen X 214. 16a. Posterior view of specimen X 215. 16b. Inner lateral view of 
specimen X 215. 16c. Aboral view of specimen X 215. 

Figs. 15, 17-19. Ligonodina levis Branson & Mehl 

15a. Inner lateral view of specimen X 207. 15b. Outer lateral view of specimen X 207. 
17a. Inner lateral view of specimen X 206. 17b. Outer lateral view of specimen X 206. 
1 8a. Outer lateral view of specimen X 205. 18b. Inner lateral view of specimen X 205. 
19a. Inner lateral view of specimen X 204. 19b. Outer lateral view of specimen X 204. 



Bull. Br. Mus. nat. Hist. (Geol. Suppl.) 5 



PLATE 26 




PLATE 27 
All specimens coated and magnified x 31.5 

Figs. 1-3. Ozarkodina plana (Huddle) 

1. Lateral view of specimen X 301. 2. Lateral view of specimen X 300. 3. Lateral view of 
specimen X 419. 

Figs. 4, 5. Ozarkodina plumula Collinson & Druce 

4. Lateral view of specimen X 302. 5a. Lateral view of specimen X 303. 5b. Aboral lateral 
view of specimen X 303. 

Fig. 6. Ozarkodina curvata Rexroad 

a. Outer lateral view of specimen X 289. b. Inner lateral view of specimen X 289. 

Figs. 7, 8. Ozarkodina macer (Branson & Mehl) 

7. Lateral view of specimen X 305. 8. Lateral view of specimen X 304. 

Figs. 9-1 1. Ozarkodina sp. 

9. Lateral view of specimen X 307. 10. Lateral view of specimen X 308. 11. Lateral view 
of specimen X 306. 

Figs. 12, 20, 21. Ozarkodina macra Branson & Mehl 

12. Lateral view of specimen X 297. 20. Lateral view of specimen X 296. 21. Lateral view 
of specimen X 298. 

Fig. 13. Ozarkodina cf. congesta Stauffer 
Lateral view of specimen X 288. 

Fig. 14. Ozarkodina cf. delicatula (Stauffer & Plummer) 
a. Lateral view of specimen X 292. b. Oral view of specimen X 292. 

Figs. 15, 19. Ozarkodina delicatula (Stauffer & Plummer) 

15a. Lateral view of specimen X 290. 15b. Oral view of specimen X 290. 15c. Aboral view 
of specimen X 290. 19a. Lateral view of specimen X 291. 19b. Oral view of specimen 
X 291. 19c. Aboral view of specimen X 291. 

Figs. 16, 17, 22. Ozarkodina hindei Clarke 

16. Lateral view of specimen X 294. 17a. Outer lateral view of specimen X 293. 17b. Inner 
lateral view of specimen X 293. 22a. Aboral lateral view of specimen X 295. 22b. Lateral 
view of specimen X 295. 

Fig. 18. Ozarkodina parva (Huddle) 
Lateral view of specimen X 299. 

Fig. 23. Ozarkodina compressa Rexroad 
Lateral view of specimen X 420. 

Fig. 24. Ozarkodina cf. elegans (Stauffer) 
Lateral view of specimen X 109. 



Bull. Br. Mus. nat. Hist. (Geol. Suppl.) 5 



PLATE 27 



1 2 3 4 




^4* »J^ «>A^ itf6&k# ^yW 




j^V <i^% 


^ 15?% 


(^■■WSife^ 20 ^¥ 




19a ^P ^ 

i9b ^^ ^^•■BS55"iP 

22a 

^ 1 iwnr V 

^^ ^22^ 





PLATE 28 
All specimens coated and magnified x 31.5 

Figs. 1-4. Prioniodina subaequalis (Higgins) 
ia. Lateral view of specimen X 344. ib. Aboral view of specimen X 344. ic. Oral view of 
specimen X 344. 2a. Lateral view of specimen X 343. 2b. Oral view of specimen X 343. 
3a. Aboral view of specimen X 341. 3b. Lateral view of specimen X 341. 3c. Oral view of 
specimen X 341. 4. Lateral view of specimen X 342. 

Fig. 5. Prioniodina oweni sp. now 

a. Lateral view of holotype X 330. b. Oral view of holotype X 330. c. Aboral view of 
holotype X 330. 

Fig. 6. Prioniodina ? sp. nov. 
a. Lateral view of holotype X 345. b. Aboral view of holotype X 345. c. Oral view of 
holotype X 345. 

Figs. 7-10. Prioniodina stipans (Rexroad) 
7a. Lateral view of specimen X 338. 7b. Aboral view of specimen X 338. 7c. Oral view of 
specimen X 338. 8a. Lateral view of specimen X 337. 8b. Aboral view of specimen X 337. 
8c. Oral view of specimen X 337. 9a. Lateral view of specimen X 339. 9b. Aboral view of 
specimen X 339. gc. Oral view of specimen X 339. 10a. Lateral view of specimen X 340. 
10b. Aboral view of specimen X 340. 10c. Oral view of specimen X 340. 

Figs. 11-12. Prioniodina laevipostica (Rexroad & Collinson) 
11. Inner lateral view of specimen X 317. 12a. Outer lateral view of specimen X 316. 12b. 
Inner lateral view of specimen X 316. 

Fig. 13. Prioniodina eireica (Collinson & Druce) 
Inner lateral view of specimen X 315. 

Fig. 14. Hindeodella sp. nov. 
a. Oral view of specimen X 186. b. Lateral view of specimen X 186. 

Figs. 15-17. Hindeodella croka Collinson & Druce 
15. Oral view of specimen X 164. 16. Oral view of specimen X 162. 17. Oral view of 
specimen X 163. 

Figs. 18-20. Hindeodella hibbardi Collinson & Druce 
18. Lateral view of specimen X 167. 19. Lateral view of specimen X 168. 20. Lateral view 
of specimen X 169. 

Figs. 21, 26. Hindeodella montanaensis (Scott) 

21. Lateral view of specimen X 175. 26. Lateral view of specimen X 176. 

Figs. 22-24, 30-3 1 - Hindeodella ibergensis (Bischoff) 

22. Lateral view of specimen X 171. 23. Lateral view of specimen X 170. 24. Lateral view 
of specimen X 173. 30. Lateral view of specimen X 172. 31. Lateral view of specimen 
X 174. 

Figs. 25, 28. Hindeodella antecomplex Collinson & Druce 
25. Lateral view of specimen X 157. 28. Lateral view of specimen X 156. 

Fig. 27. Hindeodella tenuis Clarke 
Lateral view of specimen X 187. 

Fig. 29. Hindeodella cf. croka Collinson & Druce 
Oral view of specimen X 165 



Bull. Br. Mus. nat. Hist. (Geol. Suppl.) 5 



PLATE 28 



PLATE 29 
All specimens coated and magnified x 31.5 

Figs. 1-2. Angulodtis sp. nov. D 

ia. Lateral view of specimen X 41. ib. Oral view of specimen X 41. ic. Aboral view of 
specimen X 41. 2a. Lateral view of specimen X 40. 2b. Oral view o'f specimen X 40. 2c. 
Aboral view of specimen X 40. 

Figs. 3-4. Angulodus sp. nov. C. 

3a. Lateral view of specimen X 39. 3b. Oral view of specimen X 39. 3c. Aboral view of 
specimen X 39. 4a. Lateral view of specimen X 38. 4b. Oral view of specimen X 38. 4c. 
Aboral view of specimen X 38. 

Fig. 5. Angulodus sp. nov. B. 
a. Lateral view of specimen X 37. b. Aboral view of specimen X 37. 

Figs. 6-7, 9-10. Hindeodella subtilis Ulrich & Bassler 

6a. Lateral view of specimen X 180. 6b. Oral view of specimen X 180. 7a. Lateral view of 
specimen X 177. 7b. Oral view of specimen X 177. 9. Lateral view of specimen X 178. 
10a. Lateral view of specimen X 179. 10b. Oral view of specimen X 179. 

Fig. 8. Angulodus walrathi (Hibbard) 
Lateral view of specimen X 36. 

Figs, ii, 13-15. Hindeodella secarata Collinson & Druce 

11. Lateral view of specimen X 184. 13. Lateral view of specimen X 181. 14. Lateral view 
of specimen X 182. 15. Lateral view of specimen X 183. 

Fig. 12. Hindeodella sp. 

a. Lateral view of specimen X 445. b. Oral view of specimen X 445. c. Aboral view of 
specimen X 445. 

Figs. 16-17. Hindeodella corpulenta Branson & Mehl 

16a. Lateral view of specimen X 160. 16b. Postero-lateral view of specimen X 160. 16c. 
Aboral view of specimen X 160. 17a. Aboral view of specimen X 161. 17b. Lateral view of 
specimen X 161. 17c. Postero-lateral view of specimen X 161. 



Bull. Br. Mus. nat. Hist. (Geol. Suppl.) 5 



PLATE 29 



la 2a 


t£* ♦** 


•rfpJGKiMK'*, 


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PLATE 30 
All specimens coated and magnified x 31.5 

Fig. 1. Gnathodus semiglaber Bischoff 

a. Oral view of specimen X 421. b. Aboral view of specimen X 421. c. Lateral view of 
specimen X 421. 

Figs. 2, 8. Gnathodus punctatus - Gnathodus semiglaber transition 
2. Oral view of specimen X 521. 8. Oral view of specimen X 525. 

Figs. 3, 7, 9-17. Pseudopolygnathus cf. longiposticus Branson & Mehl 

3a. Aboral view of specimen X 443. 3b. Oral view of specimen X 443. 7a. Aboral lateral 
view of specimen X 448. 7b. Oral view of specimen X 448. 9. Aboral view of specimen 
X 442. 10. Oral view of specimen X 442. 11. Oral view of growth stages of specimen X 522. 
12. Oral view of growth stages of specimen X 523. 13. Oral view of growth stages of specimen 
X 433. 14. Oral view of growth stages of specimen X 434. 15. Oral view of growth stages of 
specimen X 547. 16. Oral view of specimen X 449. 17a. Oral view of specimen X 545. 
17b. Aboral view of specimen X 545. 

Figs. 4, 5. Gnathodus sp. 

4a. Oral view of specimen X 424. 4b. Aboral view of specimen X 424. 4c. Lateral view of 
specimen X 424. 5a. Aboral view of specimen X 425. 5b. Oral view of specimen X 425. 
5c. Lateral view of specimen X 425. 

Fig. 6. Gnathodus delicatus Branson & Mehl 

a. Oral view of specimen X 426. b. Aboral view of specimen X 426. c. Lateral view of 
specimen X 426. 

Fig. 18. Gnathodus bilineatus (Roundy) transitional from G. punctatus (Cooper) 
a. Oral view of specimen X 439. b. Aboral view of specimen X 439. 

Fig. 19. Pseudopolygnathus triangulus cf. pinnatus Voges 
a. Aboral view of specimen X 502. b. Oral view of specimen X 502. 



Bull. Br. Mus. nat. Hist. (Geol. Suppl.) 5 



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PLATE 31 
All specimens coated and magnified x 31.5 

Fig. 1. Hindeodella undata Branson & Mehl 
Lateral view of specimen X 185. 

Fig. 2. Apatognathus sp. 
Inner lateral view of specimen X 318. 

Fig. 3. Hibbardella (Hassognathus) ? sp. 
Lateral view of specimen X 319. 

Fig. 4, 16. Ligonodina tenuis Branson & Mehl 

4. Lateral view of specimen X 320. 16. Lateral view of specimen X 321. 

Figs. 5, 11. Magnilaterella spp. 

5. Inner lateral view of specimen X 322. 11. Aboral inner lateral view of specimen X 323. 

Fig. 6. Hibbardella (Hibbardella) abnormis Branson & Mehl 
Lateral view of specimen X 508. 

Fig. 7, 10. Hindeodus alatoides (Rexroad & Burton) 
7. Lateral view of specimen X 193. 10. Lateral view of specimen X 192. 

Fig. 8. Hindeodus imperfectus (Rexroad) 
Lateral view of specimen X 194. 

Fig. 9. Ligonodina tulensis (Pander) 
Lateral view of specimen X 328. 

Fig. 12. Spathognathodus scitulus subsp. nov. 
a. Oral view of specimen X 390. b. Aboral view of specimen X 390. c. Lateral view of 
specimen X 390. 

Fig. 13. Cavusgnathus unicornis Youngquist & Miller 
a. Aboral view of specimen X 329. b. Lateral view of specimen X 329. 

Fig. 14. Lonchodina transitans Collinson & Druce 
Lateral view of specimen X 234. 

Fig. 15. Kladognathus mehli (Rexroad) 
Inner lateral view of specimen X 524. 

Fig. 17. Hindeodella brevis Branson & Mehl 
Lateral view of specimen X 514. 

Figs. 18, 19. Hindeodella cooperi (Elias) 
18. Lateral view of specimen X 158. 19. Lateral view of specimen X 159. 

Fig. 20. Siphonodella sp. 
Oral view of specimen X 539. 

Fig. 21. Polygnathus sp. 
a. Oral view of specimen X 130. b. Aboral view of specimen X 130. 

Fig. 22. Apatognathus sp. nov. A. 
a. Inner lateral view of specimen X 43. b. Outer lateral view of specimen X 43. 

Fig. 23. Gnathodus girtyi turritus Collinson & Druce 
a. Lateral view of specimen X 116. b. Aboral view of specimen X 116. c. Oral view of 
specimen X 116. 

Fig. 24. Geniculatus sp. 
Lateral view of specimen X 327. 

Figs. 25-26. Magnilaterella robusta Rexroad & Collinson 
25. Inner lateral view of juvenile specimen X 528. 26. Inner lateral view of specimen X 529. 

Fig. 27. Apatognathus porcatus (Hinde) 
Inner lateral view of specimen X 220. 



Bull. Br. Mus. nat. Hist. (Geol. Suppl.) 5 



PLATE 31 




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